Use GitHub Issue Labeler action instead of dotnet-issue-labeler

[lbussell]

We don't get very much value from the automatic labels provided by https://github.com/dotnet/issue-labeler.

This repo, and other .NET Docker repos, should move to a simpler approach using the GitHub issue labeler action to apply the untriaged label to all issues, and leave area-labels up to our issue triage process.