Add documentation for using .dev.vars instead of .env when deploying with Cloudflare Pages

[arkantrust]

Problem:
While integrating Clerk with Astro on Cloudflare Pages using the Cloudflare adapter, I encountered the following error: Publishable key is invalid. This issue occurred because Clerk did not recognize environment variables from .env files. As noted in Astro's documentation, some adapters, like Cloudflare, don't support the getSecret() function, which can cause issues with environment variables.

Solution:
Adding a note in the Clerk documentation for Astro would clarify that Cloudflare Pages requires environment variables to be defined in a .dev.vars file instead of .env. This will help prevent similar issues for developers working with these tools.

Where to Update:
Include this note in the Astro integration section and consider mentioning it in other relevant areas of the documentation.

I’d be happy to submit a pull request to help with this!