ci: GH-620 centralized composite action and configuration to test GHA runner labels against self-hosted runners

[Kerruba]

Related to: camunda/team-infrastructure#620.

Create a composite action to validate and lint repository workflows using actionlint.
The composite action configuration includes self-hosted runner labels supported by infrastructure team and available in Camunda

Some possible questions:

❓ Why using all the actionlint checks instead of using only the runners-label check
💬 From what I've seen in actionlint usage documentation, there's no way to limit the checks to only specific one

❓ What's the rationale behind the way actionlint is downloaded? Why not use asdf or similar approached?
💬 That's the way actionlint documentation suggest to download actionlint executable

❓ Why using a composite action instead of a reusable workflow?
💬 I was thinking of using a reusable workflow at the very beginning to solve the chicken-egg issue of running the composite action on an invalid runner. Reusable workflow would solve this indeed, but having a reusable workflow only for a single job (actionlint) seemed to me a bit too much. Also, most (if not all) the shared workflows in this repository are composite actions. Therefore I've decided to use a composite action right now, leaving the door open for a future improvement

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