lock: make --no-update the default behavior and introduce --regenerate for the previous default behavior

[radoering]

Pull Request Check List

Resolves: #3248
Relates-to: #9136

• Added tests for changed code.
• Updated documentation for changed code.

⚠️ Breaking change. Requires a major version bump. ⚠️

The most difficult decision (if we want to let this change happen) is the name of the new option (old default behavior).

The old flag was --no-update. Why not call the new flag --update?

Because it's not exactly what it is. It does not update the locked package versions but ignores the lock file and creates a new one from scratch. The result is the same as an update because our (only) locking strategy is "use-latest" but in case we introduce alternative locking strategies in the future (cf #3527) the result will be different. Further, by not calling it --update the difference to poetry update --lock becomes clearer.

[rbebb]

I believe that it's the right move to switch the default behavior of poetry lock to poetry lock --no-update. More often than not, users are looking to update a few packages rather than all of them. If a user updates all of the packages, the user has an increased risk of introducing a package update that contains breaking changes.

This change will result in a more user friendly tool since the behavior will be more clear and therefore less experienced users will have less confusion!

[rbebb]

The proposed changes look good to me! Is it a good time to mark this draft as ready for review?

[radoering]

This PR is marked as draft to avoid that it is merged by accident because we only want to do this with a major version bump and it is very likely but not absolutely clear that the next version will be 2.0. I will mark it as ready as soon as this is clarified. The actual review shoud be quite easy because this is a simple change.