Prune pipelines / pipeline runs

[michaelsauter]

Closes #153.

Tasks:

• Updated design documents in docs/design directory or not applicable
• Updated user-facing documentation in docs directory or not applicable
• Ran tests (e.g. make test) or not applicable
• Updated changelog or not applicable

[gerardcl]

so far it LGTM! If I got it right, old pipelines already existing prior upgrading to a new ods-pipeline release (that includes this PR) will need manual cleanup, right?

I added some small comments and questions and maybe I would go for adding another test with changing to different edge/expected cases with the params minKeepHours and maxKeepRuns in pruner_test.go?

but approving for now! this is looking good!! 🚀

[michaelsauter]

If I got it right, old pipelines already existing prior upgrading to a new ods-pipeline release (that includes this PR) will need manual cleanup, right?

Correct, I added a comment in the changelog regarding this.

I added some small comments and questions and maybe I would go for adding another test with changing to different edge/expected cases with the params minKeepHours and maxKeepRuns in pruner_test.go?

Good point! I added some validation to ensure minKeepHours>=1 and maxKeepRuns>=1. The logic would work also for minKeepHours=0 and maxKeepRuns=0, but I think that is unlikely to be what the user actually wanted to do, so better to prevent it.