Git Flow: coder/modules: create unified git-repo module

[johnstcn]

Builds upon #407 #406 #405 #404

Create a new unified git-flow module that comprises the functionality of both the existing git-config and git_clone modules:

data "coder_external_auth" "github" {
  id = "github"
}

module "git-repo" {
	# Base directory to clone the repository
	dir = "$HOME"
	# Set GitHub as authentication method (Optional, required for private repos)
	auth = data.coder_external_auth.github.id
	# URL for a repository. When the url is set, the user is not prompted to fill in a repo
	url = "[email protected]:coder/coder.git"
	# Branch, tag or commit hash. When ref is set, the autocomplete will not allow the user to pick a ref
	ref = "main"