Add Apitally to third party packages section in docs

[itssimon]

Summary

• Add an item for Apitally to the third party packages page in the docs.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[Kludex]

I think the third party packages is enough... No need for the middleware...

[itssimon]

Fair call. Done.

[Kludex]

Is this going to be the first commercial product included in this section?

Does it sound fair to you to promote your product without you even sponsoring the organization?

[itssimon]

I genuinely believe that this will add value to the community, despite being a commercial product.

There are a few other commercial products linked in the Third party middleware section of the docs (e.g. Bugsnag, Rollbar).

Given Apitally is built with FastAPI, and hence Starlette, I do think sponsorship would be fair regardless of this mention in the docs. I will definitely consider it once Apitally is profitable!