Added docs for the OAuth2introspection library

[wcabus]

This PR adds documentation for the ASP.NET Core OAuth 2.0 introspection authentication handler library, previously known as IdentityModel.AspNetCore.OAuth2Introspection:

• Docs added in a new folder introspection-auth-handler, which is included in astro.config.mjs
• Added a new card on the docs homepage to showcase this FOSS library
• Fixed references on identityserver/apis/aspnetcore/reference.md to the old library
• Updated the linkchecker NPM task to reflect the settings used during builds, and added an alternative that runs on Windows machines

[khalidabuhakmeh]

Should we be clear about it being "OAuth" and not just "Auth"?

[wcabus]

Should we be clear about it being "OAuth" and not just "Auth"?

You mean in astro.config.mjs? The "Auth" there is an abbreviation of "Authentication", the result of a discussion on how to format this entry in the sidebar. The other choices were too long and didn't fit on a single line.

[khalidabuhakmeh]

Maybe we should call it "OAuth Introspection"?

Another option.

[wcabus]

I can live with OAuth 2.0 Introspection as the title there.
We did have a discussion somewhere else though where the general preference was to allude that this is about an ASP.NET Core authentication handler: if we give this section a generic "introspection" title, people might think it's a library for introspecting tokens anywhere (mobile, desktop, ...)

[wcabus]

@khalidabuhakmeh How about this for the sidebar?

[maartenba]

Does the docs need updating after https://github.com/DuendeSoftware/issues/issues/457 ?

[wcabus]

Does the docs need updating after DuendeSoftware/issues#457 ?

To verify, but normally I already took into account the expected new naming.

[maartenba]

Added a few suggestions