feat(branches): add rename subcommand (#939)

Implements the 'branches rename' command to rename a branch in a repository.
This wraps the Gitea API endpoint PATCH /repos/{owner}/{repo}/branches/{branch}.

Usage: tea branches rename <old_branch_name> <new_branch_name>

Example: tea branches rename -r owner/repo main factory

This resolves issue #938.

Reviewed-on: https://gitea.com/gitea/tea/pulls/939
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Matěj Cepl <mcepl@cepl.eu>
Co-committed-by: Matěj Cepl <mcepl@cepl.eu>

cmd/branches.go

@@ -24,6 +24,7 @@ var CmdBranches = cli.Command{
 		&branches.CmdBranchesList,
 		&branches.CmdBranchesProtect,
 		&branches.CmdBranchesUnprotect,
+		&branches.CmdBranchesRename,
 	},
 	Flags: append([]cli.Flag{
 		&cli.BoolFlag{