Add Branch Specification for Plugin Installation

# Description:
The objective of this enhancement is to let users specify a branch when installing plugins using `coffee`.
> It is important to note that this proposal assumes the presence of only one plugin in each remote repository.

# Goal:
- Allow users to install a plugin from a specific branch using the command:
```shell
coffee install --branch `
```

# Existing Features:
- The `repository` struct already includes a `branch` field.
- A function, `fast_forward(path: &str, branch: &str) -> Result`, is available to facilitate fast-forwarding to a specified branch.