Versioned Storage: Git operations

[sidoruka]

Background To make the Versioned Storages (#1805) available from inside the running job - will need some service, running inside a container. This service shall the user to perform common Git operations to:

• Clone the Versioned Storage
• Commit/Push the changes to the Versioned Storage
• Resolve conflicts, if any

Approach

• A service shall be implemented as a part of the FSBrowser
• Clone operation shall accept the Versioned Storage ID and clone it (latest or a specific commit) into a pre-configured location (environment variable -> System Parameter)
• List shall allow to get all the Versioned Storages, cloned into the job
• Commit operation shall accept a commit message plus a Versioned Storage ID and perform pull, commit and push to remote
  • If any conflict is detected - it shall be reported to the client with the conflicting files diffs
  • As a result - client shall send back a resolved/fixed version of the files, which shall be committed and pushed
• At any point - client shall be able to request the diffs for a selected cloned storage
• GUI shall expose these operations for the active (RUNNING) jobs: in the Dashbord and Run Details forms. E.g.:

[NShaforostov]

Docs were added via #3217 and located here.