Add caching layer for GitLab provider, to avoid low rate limit when retrieving repository data

[gchiesa]

Description

SKA uses the GitLab API to retrieve an archive of the repository when the blueprint is requested directly from GitLab upstream.

The documentation reports that such API is rate limited to 5 reqs/minute. See here

For this reason we should implement some sort of caching that:

• retrieve to gitlab the latest commit sha for the ref used in the upstream uri
• check if there is a cache for the repository
  • if yes, validate if the cache is updated to the latest commit sha
  • if yes, then use the cache hit
• if no commit sha is matching or no repo is cached then it will perform the normal get repository archive file and store the new entity in the cache under the tuple repository,commit-sha