feat: lazy load Highcharts

[IgnaceMaes]

Implements https://github.com/ember-learn/ember-website/issues/1086

Can be testes by navigating from the homepage to the survey page, and you'll see highcharts being loaded as a separate chunk:

**Before**

``` Built project successfully. Stored in "dist/". File sizes: - dist/assets/blurhash-691e6367e568ca4be5b5a2767d815c72.js: 5.33 KB (2.29 KB gzipped) - dist/assets/chunk.143.6e0c58448e0167a30766.js: 4.02 KB (1.87 KB gzipped) - dist/assets/chunk.177.0ad8d0a09b4a9eee138e.js: 494.86 KB (130.84 KB gzipped) - dist/assets/chunk.178.51eb7bcabc085353c98d.js: 1.79 KB (919 B gzipped) - dist/assets/chunk.208.75f0333c684dfa148411.js: 138.85 KB (39.94 KB gzipped) - dist/assets/chunk.488.5727fc2e359ff31b5ce8.js: 451.8 KB (139.21 KB gzipped) - dist/assets/components/addon-tabs-ced999dc1ee0a2709b35022ac116a53a.css: 954 B (450 B gzipped) - dist/assets/components/brand-logos-12b2a07a6d74a3f34c6fa259a2b308e4.css: 456 B (237 B gzipped) - dist/assets/components/callout-banner-2eecb3ace2e5e0dbefc7e7825eaf7312.css: 715 B (372 B gzipped) - dist/assets/components/cta-emberconf-573326c0ad3a08de3b4c2d92640a834b.css: 701 B (304 B gzipped) - dist/assets/components/ecosystem-icons-1f31451a2cfa6c90d342a2af2c69f2d4.css: 609 B (296 B gzipped) - dist/assets/components/faqs-f90d5e7dfe8e6e94d3e28c741243a8a9.css: 150 B (122 B gzipped) - dist/assets/components/homepage-hero-callout-50e2535aac0836d67d030f760510e19d.css: 491 B (279 B gzipped) - dist/assets/components/homepage-image-grid-15bd5b931f1175fdc12734a917a991eb.css: 679 B (330 B gzipped) - dist/assets/components/lts-table-d951d05562803e438777215b03c73069.css: 198 B (121 B gzipped) - dist/assets/components/release-timeline-df87c719949ec7b27d095459d4b0c4ee.css: 323 B (181 B gzipped) - dist/assets/components/survey-section-d1de42891faaa3daa133dcfc0f0c0fa5.css: 606 B (306 B gzipped) - dist/assets/components/surveys-1fdd5917097beb9d1ade53ffb17e6f07.css: 455 B (257 B gzipped) - dist/assets/components/team-list-3dd36c04ffea56cc5334db830c08f732.css: 90 B (101 B gzipped) - dist/assets/components/terminal-code-7e519fd5da7aee7b86629d981fbcf0a1.css: 450 B (238 B gzipped) - dist/assets/ember-website-76d9b17c2a24c2a1dac8f5e54e8bd577.css: 9.25 KB (2.71 KB gzipped) - dist/assets/ember-website-c735bcdadd5e3a0eb8df57d0181b4cec.js: 500.75 KB (88.9 KB gzipped) - dist/assets/ember-website-fastboot-3ec4312b42e49f81b2c9be07ee8fa4ac.js: 26.46 KB (7.33 KB gzipped) - dist/assets/legacy/form-806d198f6ac471089b03d86bde752e0c.css: 2.17 KB (691 B gzipped) - dist/assets/polyfill-evergreen-2ac6bc8e6a5c535fe8849b8ff507775a.js: 89 B (104 B gzipped) - dist/assets/polyfill-legacy-f4fdd05d521698f10b24eb135c5454a7.js: 86 B (103 B gzipped) - dist/assets/polyfill-shared-861bfde4e30ecfba86fdc785567a907e.js: 9.15 KB (3.95 KB gzipped) - dist/assets/vendor-6c0828ada27008e3e2021e555322dc7d.css: 49.76 KB (10.04 KB gzipped) - dist/assets/vendor-f3ce195970ae554560e0f7dc1050ce41.js: 954.28 KB (243.3 KB gzipped) - dist/ember-fetch/fetch-fastboot-e28194c4f1288a25de407aad6f7fab09.js: 887 B (510 B gzipped) ```

**After**

``` Built project successfully. Stored in "dist/". File sizes: - dist/assets/blurhash-691e6367e568ca4be5b5a2767d815c72.js: 5.33 KB (2.29 KB gzipped) - dist/assets/chunk.143.04941bd5d6e02fcd4afa.js: 4.12 KB (1.94 KB gzipped) - dist/assets/chunk.177.0ad8d0a09b4a9eee138e.js: 494.86 KB (130.84 KB gzipped) - dist/assets/chunk.178.5172162e4debb7ef9542.js: 1.79 KB (920 B gzipped) - dist/assets/chunk.208.75f0333c684dfa148411.js: 138.85 KB (39.94 KB gzipped) - dist/assets/chunk.496.ce9752c9dad2ff1fc461.js: 31.69 KB (10.47 KB gzipped) - dist/assets/chunk.550.50f79ca7d4d83b4da056.js: 126.16 KB (33.67 KB gzipped) - dist/assets/chunk.997.8888b4b1fcb7ddd27509.js: 294.17 KB (96.35 KB gzipped) - dist/assets/components/addon-tabs-ced999dc1ee0a2709b35022ac116a53a.css: 954 B (450 B gzipped) - dist/assets/components/brand-logos-12b2a07a6d74a3f34c6fa259a2b308e4.css: 456 B (237 B gzipped) - dist/assets/components/callout-banner-2eecb3ace2e5e0dbefc7e7825eaf7312.css: 715 B (372 B gzipped) - dist/assets/components/cta-emberconf-573326c0ad3a08de3b4c2d92640a834b.css: 701 B (304 B gzipped) - dist/assets/components/ecosystem-icons-1f31451a2cfa6c90d342a2af2c69f2d4.css: 609 B (296 B gzipped) - dist/assets/components/faqs-f90d5e7dfe8e6e94d3e28c741243a8a9.css: 150 B (122 B gzipped) - dist/assets/components/homepage-hero-callout-50e2535aac0836d67d030f760510e19d.css: 491 B (279 B gzipped) - dist/assets/components/homepage-image-grid-15bd5b931f1175fdc12734a917a991eb.css: 679 B (330 B gzipped) - dist/assets/components/lts-table-d951d05562803e438777215b03c73069.css: 198 B (121 B gzipped) - dist/assets/components/release-timeline-df87c719949ec7b27d095459d4b0c4ee.css: 323 B (181 B gzipped) - dist/assets/components/survey-section-d1de42891faaa3daa133dcfc0f0c0fa5.css: 606 B (306 B gzipped) - dist/assets/components/surveys-1fdd5917097beb9d1ade53ffb17e6f07.css: 455 B (257 B gzipped) - dist/assets/components/team-list-3dd36c04ffea56cc5334db830c08f732.css: 90 B (101 B gzipped) - dist/assets/components/terminal-code-7e519fd5da7aee7b86629d981fbcf0a1.css: 450 B (238 B gzipped) - dist/assets/ember-website-76d9b17c2a24c2a1dac8f5e54e8bd577.css: 9.25 KB (2.71 KB gzipped) - dist/assets/ember-website-cb77f1d7c5bd154652110cd0b85ea776.js: 501.32 KB (88.95 KB gzipped) - dist/assets/ember-website-fastboot-3ec4312b42e49f81b2c9be07ee8fa4ac.js: 26.46 KB (7.33 KB gzipped) - dist/assets/legacy/form-806d198f6ac471089b03d86bde752e0c.css: 2.17 KB (691 B gzipped) - dist/assets/polyfill-evergreen-2ac6bc8e6a5c535fe8849b8ff507775a.js: 89 B (104 B gzipped) - dist/assets/polyfill-legacy-f4fdd05d521698f10b24eb135c5454a7.js: 86 B (103 B gzipped) - dist/assets/polyfill-shared-861bfde4e30ecfba86fdc785567a907e.js: 9.15 KB (3.95 KB gzipped) - dist/assets/vendor-9ab8028c33affe0479ee6dd6a798853e.css: 49.76 KB (10.05 KB gzipped) - dist/assets/vendor-f3ce195970ae554560e0f7dc1050ce41.js: 954.28 KB (243.3 KB gzipped) - dist/ember-fetch/fetch-fastboot-e28194c4f1288a25de407aad6f7fab09.js: 887 B (510 B gzipped) ```

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