As zuliprc files are in a standard format that you can access from
any programming language, not just Python, it makes more sense to
have them documented with the information about API keys.
Fixes#10670.
- Adds instructions for downloading a zuliprc file for a bot or for
yourself.
- Updates the button label to "Download zuliprc", since that's the
filename it downloads.
Fixes#28881.
- Updates `.prettierignore` for the new directory.
- Updates any reference to the API documentation directory for
markdown files to be `api_docs/` instead of `zerver/api/`.
- Removes a reference link from `docs/documentation/api.md` that
hasn't referenced anything in the text since commit 0542c60.
- Update rendering of API documentation for new directory.
