Added branch functionality to forge init command

[janbro]

Motivation

Implements feature #5687 which allows a branch argument to be passed when initializing a forge repository from a template. Adds an additional argument branch which requires the template argument to exist.

Solution

forge init --template foundry-rs/forge-template --branch [branch_name]

[janbro]

In implementing this, I believe I uncovered a bug with how the template command logic resets the git history. The following code does not remove the .git directory from the correct root folder and operates on the CWD. Let me know if this context issue should be addressed in this PR or another issue should be opened.

foundry/crates/forge/bin/cmd/init.rs

Lines 60 to 71 in bff4ed9

	p_println!(!quiet => "Initializing {} from {}...", root.display(), template);
	Git::clone(shallow, &template, Some(&root))?;
	// Modify the git history.
	let commit_hash = git.commit_hash(true)?;
	std::fs::remove_dir_all(".git")?;
	git.init()?;
	git.add(Some("--all"))?;
	let commit_msg = format!("chore: init from {template} at {commit_hash}");
	git.commit(&commit_msg)?;

[Evalir]

lgtm! we can tackle what you found in another PR, thank you!