Expose "cache-key" as an output of cache-restore

[danwulff]

Description:

While the cache-hit output tells us whether a cache was found, the action currently does not expose which "cache key" was used.

Justification:

A cache-key could be helpful to manually purge caches created in a pull request upon pull request closure. In very active repos, 10GB cache limit could cause the default branch cache to be purged prior to pull request (branch) caches. Providing a cache-key would allow folks to choose whether to purge caches manually. Combined with https://github.com/actions/setup-node/issues/663 this could give users more flexibility in controlling caches.

Are you willing to submit a PR?

Yes, I'll see if I can find some time create a PR.

[aparnajyothi-y]

Hello @danwulff, Thank you for creating the issue and we will get back to you once we have some feedback on this :)