Add GitHub actions to test ESP builds as a automated merge check for PRs

[tmcadam]

This contains a simple github action that runs a pio run on pushes to either main or any branch beginning with dev-esp. This will test that all ESP targets compile. This can be configured as a branch protection for main meaning any PR to main must have a successful run of this action, before the merge button is enabled (override is possible by admins).

The binaries produced by pio run are discarded.

Based on: https://docs.platformio.org/en/stable/integration/ci/github-actions.html#using-cmd-run-command

Other automated checks we could consider are:

• run the same check with the stm32 tergets
• check that debug is disabled in all hal files

This has been tested and is ready to merge. Once merged it won't have any impact on current workflows until enabled as a branch protection in the Github GUI.