Consider not-run checks as meeting Maestro policy

[premun]

As discussed in https://github.com/dotnet/arcade-services/pull/3636 and in https://github.com/dotnet/arcade-services/pull/4026, we have problems with Maestro checks not going green when a build is skipped. We should consider not-run builds as successful but we need to avoid cases where the check is neutral because it hasn't started yet (briefly after a commit is pushed or PR is created).

Example: https://github.com/dotnet/sdk/pull/43972

Goal

It seems that we could check the conclusion as well as the status field for that (from the other PR conversation):

"checkRuns": {
  "nodes": [
    {
      "name": "sdk-unified-build",
      "status": "COMPLETED",
      "conclusion": "NEUTRAL"
    },
}

So we need something like https://github.com/dotnet/arcade-services/pull/4026 but also verifying the status of the check.

[premun]

@MiYanni @marcpopMSFT there were way too many PRs and issues around this problem. I created this one issue to track this from now on. The rest was mostly closed already.

We will try @MiYanni's proposal from https://github.com/dotnet/arcade-services/pull/4026#issuecomment-2445455192

[premun]

AllChecksSuccesfull will be going away with https://github.com/dotnet/arcade-services/issues/4914