Add support for allowlist and/or blocklist jobs

[rytswd]

This project currently assumes all of the jobs need to pass. It's probably useful to have a whitelist / blacklist feature to suppress some errors that are irrelevant.

[rytswd]

Thanks to @tekiflo , "blocklist" (renamed for better inclusivity) has been added with ignored field 🎉

As to "allowlist", there will be a question how "allowlist" + "blocklist" would work together. If defined in both lists, should that be allowed, or blocked?

Merge Gatekeeper aims to be a "simple" solution, which you can simply copy/paste the simple YAML provided in this repo, and you are all set. For some certain scenarios, list of ignored jobs makes perfect sense, and gives the great flexibility of how you deal with Merge Gatekeeper.
With more complexity such as "allowlist" + "blocklist", it can look unnecessarily overwhelming, and without right terminology, it could well be confusing how those configurations should be handled.

The list of "ignored" jobs makes sense perfectly (again, thanks for coming up with that name, @tekiflo ☺️). This is already a great addition, and I will mark this ticket closed. For the "allowlist" setup, I am creating a new ticket separately, so that anyone keen to get that feature added can react to it, and also chime in with what makes most sense for such setup 👍