git: Create auto gitImplementation

[pjbgf]

Flux supports two git implementations: libgit2 and go-git. They do not have feature parity, which the two main problems being:

• Shallow clones is only supported by go-git. Which results in less data being transmitted through the network at every clone operation.
• Git V2 Protocol is only supported by libgit2. Servers that only support this protocol (e.g. Azure DevOps) won't work with go-git.

We should build a third git implementation type (a.k.a auto), which removes the need from users to understand the difference between the implementations, and always try to use whichever is the most optimal.

On a high-level, the new implementation could take into account:

• Server fingerprint: query the SSH banner and HTTP headers.
• Protocol Awareness: find ways to identify what Git protocol version is being used, which may be easier over HTTP scheme.

[aryan9600]

I think we should close this issue as we have removed the libgit2 git implementation from both source-controller and image-automation-controller.

[pjbgf]

Agreed, closing it. 👍