Decouple logic and periodic scheduling from internal tasks

[ferranbt]

📝 Summary

This PR decouples some internal logic in Housekeeper and API in two functions, one with the core logic and another one that decides whether the core logic is executed or not given the slot.

📚 References

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✅ I have run these commands

• [x] make lint
• [x] make test-race
• [x] go mod tidy
• [x] I have seen and agree to CONTRIBUTING.md

[metachris]

I think the direction makes sense. I feel it's a bit confusing to split these up into a function with the same name but BySlot suffix, when really it does the execution but without the prechecks.

I would prefer to be more explicit and use WithoutChecks as suffix.