ci: support for "skip-ci" github label in order to reduce what to run

[v1v]

What

skip-ci label will only run the linting stage and then will stop doing anything else.

Why

See the below use case:

As a developer, I don't want to run CI because I'm sure is going to fail and will just waste CI cycles

Issue

Similar to elastic/beats#21377

UX

See the below comment that points to the reason for the failure:

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2022-03-01T11:51:14.969+0000

• Duration: 20 min 23 sec

Test stats 🧪

Test	Results
Failed	0
Passed	524
Skipped	1
Total	525

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[v1v]

/test

[endorama]

Out of curiosity, is not possible to report it as skipped instead of errord?

[v1v]

If so, then GitHub checks will be passed

and as consequence, there is a possibility the PR could be accidentally merged without running everything in the CI.

I'm inclined to be explicit with an artificial failure to avoid the above if it makes any sense.

[endorama]

cc @mtojek

[mtojek]

Hold on folks, why is it necessary? What's the issue we're trying to solve?

[v1v]

@mtojek , the why section in the description contains the reason, I kindly raised this based on the feedback from @endorama , you can freely close it if it's not needed :)

[mtojek]

I see now, thanks for pointing it out, Victor. I believe that in the case of the Add GCP test package the problem is that we're waiting for the release v8.0.1, which should happen really soon. I wouldn't like to consider it as a justification to disable all tests, including successful ones.

If this is the only reason why we need this PR, I would be for not merging it.