Use custom templates for 1ES Pipeline Templates

[lbussell]

This PR:

• Should fix https://github.com/dotnet/dotnet-docker/issues/5332
  • It's hard to validate that it actually fixes this. However I've got a totally green build from dotnet-docker-nightly-playground here [internal link]. I think it is ignoring the /versions directory correctly.
• Reduces lots of duplication
• Centralizes the location where we define which pool we use for SDL stages
  • We could probably do better with the definition. I put it in a parameter, since parameters let you hold arbitrary yaml objects. However we could just inline the whole thing and put all the values in variables.

[dotnet-issue-labeler[bot]]

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