Add container.FilterSlice function

[oliverpool]

---

Many places have the following logic:

func (jobs ActionJobList) GetRunIDs() []int64 {
	ids := make(container.Set[int64], len(jobs))
	for _, j := range jobs {
		if j.RunID == 0 {
			continue
		}
		ids.Add(j.RunID)
	}
	return ids.Values()
}

this introduces a container.FilterMapUnique function, which reduces the code above to:

func (jobs ActionJobList) GetRunIDs() []int64 {
	return container.FilterMapUnique(jobs, func(j *ActionRunJob) (int64, bool) {
		return j.RunID, j.RunID != 0
	})
}

(I noticed this pattern while looking at #29515)