FEATURE: migrate gitea integration from http APIs to git2 library

[Masber]

manta currently relies on gitea APIs to fetch commit id information, this is quite limited because we lack of features in gitea API ( can't get the commit id related to a branch or tag name). Also CFS will be integrated with external git repos meaning gitea won't be the only source from where CFS sessions can clone from.

To simplify current limitations, we want to integrate git repo operations using git2 library.