filter output column to print only cache entry key

[lavigne958]

Describe the feature or problem you’d like to solve

Offer an option to only print the cache entry key

Proposed solution

It will benefit the users as one of the common use case is to list the keys, then to delete them.
In order to execute that step we pipe the output of the command to cut -f 1 which will only select the first column.
gh-action-cache can easily do it using some flags like --output keys which only prints the keys of each cache entry instead of the whole line.

this is how it is advertised on github documentation: https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#force-deleting-cache-entries

Additional context

Listing cache entries is very useful, in my case it was for deleting the cache entries, I am sure for most people it is too but possibly the listing is used for other reasons.

If that's open for external contribution I wish to give it a try and propose a pull requests.