LTS awareness

[rarkins]

Describe the proposed change(s).

Today in several ecosystems we treat LTS as stable and non-LTS as unstable. We should change this so that LTS and stable are different concepts and able to be controlled separately.

• Add an optional isLts boolean flag to releases returned from datasources. If a datasource has LTS awareness then it should return a value (true or false) for isLts for all releases.
• Apply these changes to the node-version datasource so that it no longer returns isStable and instead returns isLts using the same logic
• Add new, optional isLts() function to versioning modules which returns a boolean result
• Rewrite debian versioning so that the isStable() no longer returns true because a release is non-LTS, instead add an isLts() function which uses that logic
• Model new isLts logic in the worker modules on isStable, e.g. a function called isReleaseLts() which can return true, false or null
• Add a new repo config option updateToNonLts which defaults to "auto" but has options "always" or "never"
  • If auto, it means that releases with itLts=false will be ignored unless the current version/release also has isLts=false
  • If always, it means that all releases are allowed, and isLts is ignored
  • If never, it mans that releases with isLts=false are always ignored, no matter what
  • Option has no effect if the datasource/versioning has no LTS awareness

[HonkingGoose]

I found another issue that seems a bit related, it mentions LTS anyways:

• node versioning: Use the exact release that started LTS #9716

[rarkins]

To update:

• node_version datasource
• unity3d datasource
• node versioning
• ubuntu versioning