Add BitBucket Server to list of API resources

What does this MR do and why?

On the API resources overview page, we list Import repository from GitHub

The page that we redirect contains information about Importing from GitHub and BitBucket Server (further down).

This MR adds Import repository from Bitbucket Server (linking to https://docs.gitlab.com/ee/api/import.html#import-repository-from-bitbucket-server) to the list of API resources and adds the necessary anchors.

Screenshots or screen recordings

N/A

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.