Adds initial gitlocal CLI and core functionality

Introduces the `gitlocal` command-line tool for managing nested Git repositories.

Includes the following main commands:
- `convert`: Renames `.git` to `.gitlocal`, allowing a parent repository to ignore the converted child repository. Supports recursive scanning and dry-run options. Tracks converted repositories in a global configuration.
- `revert`: Restores `.gitlocal` to `.git`. Includes an option to revert all tracked repositories.
- `status`: Displays a list of all repositories currently tracked by `gitlocal`, showing their path, conversion time, and original remote/branch.

Establishes internal modules for Git operations, configuration management, and recursive repository scanning.
Adds a comprehensive test suite covering core command logic and utility functions.
Initializes Go module and basic project `.gitignore`.

main.go

@@ -0,0 +1,7 @@
+package main
+
+import "git.membo.co.uk/dtomlinson/gitlocal/cmd"
+
+func main() {
+	cmd.Execute()
+}