Update GHA tests to return single pass/fail signal at the end

Before this PR, we stored a list internally of tests that must pass on presubmit and tried to keep it up to date.

This PR moves that information keeping into GitHub by adding a 'continuous-only' variable to most testing matrices to allow authors to specify which of their tests should be skipped on presubmit. During presubmit, tests that were specified to not run on presubmit will not be run and their names will be prefixed with "[SKIPPED]". All continuous only tests will be suffixed with "(Continuous)".

At the end of running all the tests, we have a single "All Blocking Tests" signal that will tell us whether all of the necessary tests have passed (either for presubmit or continuous based on how the test was triggered).

I've tested this from a different branch [here](https://github.com/protocolbuffers/protobuf/actions/runs/9602443750?pr=17151) and from a different fork [here](https://github.com/protocolbuffers/protobuf/actions/runs/9602554500?pr=17192). These should be the same and are as far as I can tell.

I also have a continuous test run [here](https://github.com/protocolbuffers/protobuf/actions/runs/9603824200) which runs the entire test suite.

Closes #17198

PiperOrigin-RevId: 662940724