Get "associated PR for commit" working on all providers that don't have it

[sergeibbb]

Roadmap

• getPullRequestForCommit
  • azure
  • bitbucket
  • Show message about enabling an app for Bitbucket and sending to docs
  • bitbucket DC
• getAccountForCommit
  • azure
  • bitbucket
  • bitbucket DC

Related PRs:

• Add GitLens troubleshooting guide for Bitbucket pull requests gitlens-docs#109
• Implements getPullRequestForCommit and getAccountForCommit for Azure and Bitbucket #4243

Description

Associated PRs don't show up on commits because getProviderPullRequestForCommit isn't implemented (for BitBucket, Azure, possibly others)

For Bitbucket.org we need to warn user that an action is required in order to get PR info:

Verification steps

• connect Azure integration
• go to GitLens branches or remotes views
• open branches one by one until it hits getAccountForCommit
  • check that it receives the account
  • check that it does not live author avatar without any image (it could happen when if we use Azure's avatar URLs which reject anonymous access)
• open commits one by one
  • check that it hits getPullRequestForCommit
  • repeat until some commits give a PR result
  • and others don't give any result
• repeat these steps for Bitbucket and Bitbucket DC