✨ feat: allow setting template source via `!git clone`

[evolvewithevan]

✨ feat: allow setting template source via !git clone

Description:
Enable the ability to set the source repository for a template using a simple !git clone <url> command. This will define the upstream template location. Future updates to the template can be fetched with a straightforward git pull.

Current functionality is based around the command "applytemplate "

Acceptance Criteria:

• Support !git clone <url> to initialize and track a template repository
• Allow reapplying updates via git pull without breaking the local template
• Show helpful error if git pull is used before a !git clone has been run
• Optional: Allow specifying a branch (e.g. !git clone -b main <url>)
• Warn users when other git commands are tried that only git pull and git clone is supported as of now

Benefits:

• Increased familiarity with devs
• Reduces the UX complexity when reapplying templates