Reuse existing git repositories

[Angelmmiguel]

Is your feature request related to a problem? Please describe.

When using Wasm Workers Server with a remote git repository, I always have to clone it entirely. For some large repositories, cloning may take long time. Even with this repository, it takes some seconds to clone it:

$ wws https://github.com/vmware-labs/wasm-workers-server.git \
  --git-folder "examples/js-basic" -i

Describe the solution you'd like

I want wws to reuse the previously cloned repository instead of pulling it every time I run the command. To avoid having a stale repository, it should pull the latest changes. There's a pull example in the git2-rs repository.

For now, a fast-forward approach should be enough. If the repository is "dirty" and the merge fails, you will need to delete the project folder and clone it again. You can always do the merge manually.

Describe alternatives you've considered

The alternative is to keep the current approach. We may end up with conflicts, but for most cases this improvement is very convenient.

Additional context

No response