Support only running jobs for affected packages

[jakemac53]

The jobs for a package should only run if:

• Some file in the package directory changes
• There is a dependency_override which is a path to somewhere in the repo, and some file in that directory changes.
• Note that we need to look at pubspec_overrides.yaml as well as the pubspec to determine overrides.

Implementation-wise, github appears to only support this for entire workflows. We should consider if a separate workflow needs to be generated per package in the repo. This would reduce our ability to group tasks across packages though, so we would have more jobs, which might be fine. Alternatively there are some actions out there than support doing this for individual jobs (basically you have a job that checks if the modified files are in the list of ones you care about, and then your actual job only runs based on the output of that job).

[jakemac53]

Here is an example diff of how we could do this using a custom action to compute the diffs and create variables for each package that we can use in ifs for those jobs master...jakemac53:mono_repo.dart:smart-actions

[kevmoo]

Ooo! I guess we could make the generator smart to look for path dependencies to kinda force a "transitive" logic, right?

[jakemac53]

Ooo! I guess we could make the generator smart to look for path dependencies to kinda force a "transitive" logic, right?

Yes exactly