provide a save-cache-always setting

[tomsit-ionos]

Is your feature request related to a problem? Please describe.

When the WF fails, then the maven cache is being invalidated.
This is and needles and very bothersome due to cluttered logs when trying to fix an issue.

Describe the solution you'd like

I believe it is save to turn on the new cache 4.x feature by default -- or at least provide an option to set it.

I had seen this post https://stackoverflow.com/a/78376459/405749 this no-brainer ... until i learned that the setting got removed again. Hence i struck out my suggestion above.

However, there is this guide: https://github.com/actions/cache/blob/main/save/README.md#always-save-cache on how to do i for now.
My guess is, that it's not a no-brainer anymore but maybe there is a way.

Describe alternatives you've considered
I guess it's possible to configure an extra instance of the cache , but that is
a) discourages
b) redundant

Additional context

• Save cache even if a build fails leanprover/lean-action#65