Add pipeline for publishing pre-release builds

[benmcmorran]

No description provided.

[benmcmorran]

I'd like to merge as-is to main (unless signing approval comes back very quickly). No publishing of test signed bits will happen because the publishing PAT isn't wired up yet, and it will give us a few days to make sure the pipeline is scheduled as expected before publishing for real.

[gcampbell-msft]

I think that sounds reasonable

[benmcmorran]

For anyone reviewing, the failure on the vscode-arduino-prerelease check is expected. It failed while running vsce publish because there's currently no publishing PAT set on the pipeline. I'll set the PAT a few days after merging once we have confidence that the artifacts the pipeline is producing look correct.