i18n: Ensure i18n loader is included in the production build

[yuliyan]

Changes proposed in this Pull Request:

https://github.com/Automattic/wc-calypso-bridge/pull/1472 introduced loading translations for lazy loaded JS modules using @automattic/i18n-loader-webpack-plugin and a custom i18n loader module.

However, due to loadTranslations function from the i18n loader being used only in the runtime template, it got removed from the production build by Webpack's tree-shaking, which resulted in errors in the console when trying to fetch the translations.

This PR introduces some changes to ensure that the function is preserved in the production build and can be used in the runtime template.

• [ ] This PR is a very minor change/addition and does not require testing instructions (if checked you can ignore/remove the next section).

How to test the changes in this Pull Request:

• [ ] Have you followed the Writing high-quality testing instructions guide?

1. Checkout the branch locally.
2. Build the app locally with npm run build.
3. Sync the changes to your test site by following the instructions from pdDOJh-3ob-p2.
4. Change the language of your test site to any Mag-16 language.
5. If your test site is not on Ecommerce Trial plan, override the isEcommercePlanandisEcommercePlanTrialparams totrue` in class-wc-calypso-bridge-shared.php.
6. Navigate to /wp-admin/admin.php?page=wc-admin&path=%2Fmarketing and confirm strings are rendered translated.

Other information:

• [ ] Have you added an explanation of what your changes do and why you'd like us to include them?
• [ ] Have you written new tests for your changes, as applicable?

FOR PR REVIEWER ONLY:

• [ ] I have reviewed that everything is sanitized/escaped appropriately for any SQL or XSS injection possibilities. I made sure Linting is not ignored or disabled.

[github-actions[bot]]

Size Change: +657 B (+0.33%)

Total Size: 200 kB

Filename	Size	Change
./build/53.js	1.08 kB	+37 B (+3.53%)
./build/index.js	126 kB	+521 B (+0.42%)
./build/payment-gateway-suggestions.js	6.56 kB	+99 B (+1.53%)

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `./build/index.css` | 883 B | | `./build/marketing.js` | 58 kB | | `./build/payment-gateway-suggestions.css` | 1.25 kB | | `./build/plugins.js` | 3.92 kB | | `./build/style-index.css` | 2.15 kB | | `./build/style-marketing.css` | 805 B |

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