Migrate to the Locker GitHub action for locking closed/stale issues/PRs

[jeffhandley]

This migrates away from the FabricBot implementation of a scheduled search over closed issues and adopts the Locker GitHub action authored by the VS Code team. The updated fabricbot.json was generated via dotnet/fabricbot-config#83. The workflow file was implemented and tested at https://github.com/dotnet/fabricbot-config/blob/main/.github/workflows/locker.yml.

Since this workflow uses the actions/checkout action, the following GitHub Actions settings must be enabled (this has already been confirmed):

1. Allow enterprise, and select non-enterprise, actions and reusable workflows
2. Allow actions created by GitHub

After this is merged, there will only be 1 FabricBot feature still in use within this repository that needs migration, which is usage of 'noActivitySince' within event triggers.

[wtgodbe]

Looks good to me!

[jeffhandley]

Heads-up @danmoseley and @wtgodbe -- I fired the action off after merging, with the settings of locking issues/PRs that have been closed and stale for 60 days. It found a lot of matches. I overlooked one detail of the previous configuration: it was only running for issues. I apologize for that oversight.

'Locker' (as implemented) does not differentiate between issues and PRs; it just runs over both every time. Is it OK for PRs to start to get locked as well, or would you like me to revert this and go with a different approach for locking issues?

Edit: I've disabled the workflow for the time-being until we decide on this.

[ghost]

Hi @jeffhandley. It looks like you just commented on a closed PR. The team will most probably miss it. If you'd like to bring something important up to their attention, consider filing a new issue and add enough details to build context.