Add support to specify list of jobs rather than waiting for all jobs

[rytswd]

This is essentially a mirror of #17. We have got the "ignored" list where some jobs can be ignored from Merge Gatekeeper checks. It will clearly be a great addition to have an extra control to list jobs that should be checked rather than checking all jobs.

Some discussion points for this support:

• Name for the flag - the ones ignored are handled as "ignored"; words such as "included" may be clear enough?
• When the job is specified for both lists (ignored and included), it is arguable how this should be handled. It can be 1.) a configuration error and fail with such message, 2.) ignored gets precedence, 3.) included gets precedence, 4.) determined by another flag to handle which one gets precedence.

[idoqo]

I think dealing with "ignored" + "included" adds extra complexity as you mentioned in #17.

Maybe it makes sense to fail with a validation error in that case? GitHub fails similarly with paths and paths_ignored (https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#onpushpull_requestpull_request_targetpathspaths-ignore).

[rytswd]

Sorry for getting back to this late, and thanks for providing your thought @idoqo!

The "path_ignored" is the control used by GitHub, but because it completely stops all the GitHub Action run, I do not think it is a feasible approach for Merge Gatekeeper.

As of now, looking at the reaction to this issue, there is probably no strong interest for this feature from the community. We want Merge Gatekeeper to be the simple solution, and "just work" without any configuration in most cases. We could provide optional configurations, but even if it's optional, that will be an extra complexity that may be unsuitable. From that sense, we will park this ticket aside for now, and will come back to this when there are more interests in supporting this feature.