fix(core): add missing sitemap path and change base url

[chanceaclark]

What/Why?

Forgot to add back the /sitemap.xml path when doing the previous refactor. Also, uses the VERCEL_PROJECT_PRODUCTION_URL system environment variable to ensure we are using the right origin (previously it was the vercel deployment url with the hash).

Testing

https://catalyst-latest-git-fix-robots-bigcommerce-platform.vercel.app/robots.txt

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Name	Status	Preview	Comments	Updated (UTC)
catalyst-latest	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jul 10, 2024 2:17pm

6 Skipped Deployments

| Name | Status | Preview | Comments | Updated (UTC) | | :--- | :----- | :------ | :------- | :------ | | **catalyst** | ⬜️ Ignored ([Inspect](https://vercel.com/bigcommerce-platform/catalyst/DsSPqakBTraHTR4AVbkp1pcmou8s)) | | | Jul 10, 2024 2:17pm | | **catalyst-1millionproducts-store** | ⬜️ Ignored ([Inspect](https://vercel.com/bigcommerce-platform/catalyst-1millionproducts-store/Aid8TWavUAnjUM6jT9ZZZJcgws3t)) | | | Jul 10, 2024 2:17pm | | **catalyst-au** | ⬜️ Ignored ([Inspect](https://vercel.com/bigcommerce-platform/catalyst-au/FWD3fUDMsvystoPSDD7V5tXF6f22)) | [Visit Preview](https://catalyst-au-git-fix-robots-bigcommerce-platform.vercel.app) | | Jul 10, 2024 2:17pm | | **catalyst-test-store** | ⬜️ Ignored ([Inspect](https://vercel.com/bigcommerce-platform/catalyst-test-store/82p9w7UDyvahFsNQxjHpr9P2maP1)) | [Visit Preview](https://catalyst-test-store-git-fix-robots-bigcommerce-platform.vercel.app) | | Jul 10, 2024 2:17pm | | **catalyst-uk** | ⬜️ Ignored ([Inspect](https://vercel.com/bigcommerce-platform/catalyst-uk/C5wpGMZU5JabpGFRiPJ3usBC2vne)) | [Visit Preview](https://catalyst-uk-git-fix-robots-bigcommerce-platform.vercel.app) | | Jul 10, 2024 2:17pm | | **catalyst-unstable** | ⬜️ Ignored ([Inspect](https://vercel.com/bigcommerce-platform/catalyst-unstable/567y8k9sDH3ruiCPhkTswTLvCTwn)) | | | Jul 10, 2024 2:17pm |

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⚠️ No Changeset found

Latest commit: dad2ff13d0f8f081f5c1b8ca282f45ec5f7982db

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⚡️🏠 Lighthouse report

Lighthouse ran against https://catalyst-latest-q7c4wbwib-bigcommerce-platform.vercel.app

🖥️ Desktop

We ran Lighthouse against the changes on a desktop and produced this report. Here's the summary:

Category	Score
🟢 Performance	99
🟢 Accessibility	100
🟢 Best practices	96
🟠 SEO	82

📱 Mobile

We ran Lighthouse against the changes on a mobile and produced this report. Here's the summary:

Category	Score
🟠 Performance	89
🟢 Accessibility	100
🟢 Best practices	96
🟠 SEO	85