Enhancement list for VS insertion PR tagger

[allisonchou]

Pipeline: https://devdiv.visualstudio.com/DevDiv/_release?definitionId=3293

Enhancement list (thanks to Joey for helping think of these):

• Include VS Insertion PR URL in the issue body, noting that it is Microsoft only
• Collect all the inserted PR authors and add them as assignees to the issue or otherwise tag them in the issue
• Label the inserted PRs as vs-inserted
• Output the generated issue URL
• Close issues automatically (via FabricBot) ([FabricBot] Automatically close generated PR tagger issues roslyn#63040)
• Convert Merge PR < > links (generated if merged PR was a fast-forward) to use PR title instead
• Use a bot to generate PRs instead of individual credentials
• Mark insertions into other repos (e.g. dotnet/sdk repo for F#)
• Switch to using a single pipeline instead of multiple via yml file - https://docs.microsoft.com/en-us/azure/devops/pipelines/process/pipeline-triggers?view=azure-devops
• Switch to using OctoKit - https://octokitnet.readthedocs.io/en/latest/getting-started/
• Set milestone on PR for which VS version it went into

[rainersigwald]

I think I would actually prefer comments on each PR instead of a new issue linking the PRs--would that be possible/desirable for others?