feat: use GitHub Actions cache to persist the CernVM-FS cache

[wdconinc]

No description provided.

[ocaisa]

Suggested change

	key: cvmfs-cache-${{ steps.lsb-release.outputs.id-release }}-${{ steps.lsb-release.outputs.arch }}-${{ hashFiles('action.yml') }}
	key: cvmfs-cache-${{ steps.lsb-release.outputs.id-release }}-${{ steps.lsb-release.outputs.arch }}

as seen in #40, using ${{ hashFiles('action.yml') }} as part of the key is not reliable as the file being hashed as very unlikely to appear in other repositories and causes caches to always miss.

[vvolkl]

Suggested change

	${{ inputs.cvmfs_cache_base }}
	${{ inputs.cvmfs_cache_base }}

One further issue may be that the cache directory is used for a number of locks and marker files that we may not want to cache. I think in the end you only want to keep the actual data files in the hash directories ./00/ ... ./ff and maybe the ./cachedb file.

I'll test a few configurations to see what works best.