Implement basic git fetching mechanics in buildless serverless

[kwiatekus]

Description

Ensure customer's code is mounted in the right place and moment in git functions. Implement the first working version (with only public repos in the scope) that doesnt use orphaned libgit2 library anymore (see POC)

AC

• implement watching logic - controller needs to know when to fetch new revision
• a new pod must have git sources (handler and dependencies) mounted
• support public repos only (git authorisation will come later)

Reasons
Part-of #1315