Add cache-save: false option

[akx]

Description

This PR adds a new cache-save: false option to opt out of saving the cache. As described in the documentation:

For some scenarios, it may be useful to only save a given subset of dependencies,
but restore more of them for other workflows. For instance, there may be a heavy
extras dependency that you do not need your entire test matrix to download, but
you want to download and test it separately without it being saved in the cache
archive for all runs.

To achieve this, you can use cache-save: false on the run that uses the heavy
dependency.

Related issue

I only found the related issue after implementing this: #751.

Check list

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

[akx]

Rebased on v5.

@dmitry-shibanov Could you review this, please?