Extract and publish @spotlightjs/astro package

[Lms24]

We want to extract the Astro integration from the website package and make it a proper Astro integration package.

For the package to work properly with the npx astro add command, we need to keep a few things in mind:

• The integration factory function needs to be the default export of the package
• keywords need to be set according to the integrations guide
• Other fields mentioned in the guide should also be set
• AFAICT, we technically don't need to transpile to JS and we should be good to simply publish the TS source files. (Astro will bundle the integrations in its build). Let's see if this actually works.

Note: We can also first simply extract the package and worry about the package.json, keywords, etc later.