Improve cache subscriptions

[beshanoe]

Description

The idea is to further improve the cache subscriptions mechanism, namely the one which allows us to save the last state of the monorepo and run tasks only over the changed files after it. It somewhat worked already, but one of the bugs was that if the output files of the task were removed, Garment would still think the project is consistent because the input files haven't been changed. I addressed it by creating a subscription for each output file, so if the output has been removed or manually changed, Garment would rerun the whole task. In the future we can also make it rerun the task only for the particular file responsible for that changed output.
During the work, I also noticed some major flaws in the mechanism and fixed them too.

Fixes # (issue)

How Has This Been Tested?

Only manually in the Garment repo itself

Checklist:

• [ x] My code follows the style guidelines of this project
• [ x] I have performed a self-review of my own code
• I have added tests to cover my changes
• I have made corresponding changes to the documentation

Disclaimer

By sending us your contributions, you are agreeing that your contribution is made subject to the terms of our Contributor Ownership Statement