at_mono: Downstream integration tests with linked dependencies

[XavierChanth]

lead: @XavierChanth

The goal is to rerun our various test suites using linked dependencies in at_mono.

Requires #28 to be completed first.

What needs to be done:

• Create workflows in at_mono to call tests from each module
• Setup cross-repo workflow triggers like in these demo repos:
  • cross-actions-sender and cross-actions-receiver

Eventually:

• matrix builds to test various combinations of trunk vs latest (and maybe vs n-1).
  • (This requires modification/extension of melos tooling)

[XavierChanth]

Backlogging to focus on docs site

[XavierChanth]

I'm going to close this issue. While it is something potentially useful, it adds a lot of complexity and isn't really needed at this time.