Add cache-restore-only input

[dsame]

Description:

The use-cases are:

• hitting storage with few huge caches
• running build/test workflows in the parallel Add option to restore cache only #316 (comment)

The suggested workaround does not really work because it requires the users to re-engineer and reconstruct the automatically created cache key

To avoid it i introduced new input cache-restore-only that makes build to skip caching without making user to deal with cache key

Related issue:
link to the related issue.

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

[freeformz]

Yes please. I understand the arguments against, but respectfully disagree - it's a pita to have to reverse engineer the key setup and copy it into a ton of different repo workflows. And then there is the possibility of future changes. I'd like the setup-go action to "just handle all of that". i.e. I think the complexity should be shifted away from users.

[gregwebs]

Can this PR get reviewed? A use case I have for this is to be able to speed up deployments. Currently waiting for the go cache cleanup to push at the end adds a noticeable delay and the deployment build is not going to produce a useful cache that doesn't already exist. I am looking to see if it is spending time caching unnecessary things and if there are settings for that, but would be nice to avoid altogether in this case.