feat: add shuttle extensions cli commands

[kjuulh]

This adds a basic command palette for shuttle such as:

• shuttle ext update
• shuttle ext init
• shuttle ext install

This also right now uses a skeleton implementation of a central ExtensionManager which is supposed to orchestrate these extensions. The call to the extensions will be done in a later PR

Builds on: #219

[kjuulh]

@lunarway/squad-aura I really like to get this merged before hackathon.

I am opening up the PRs now (stacked), They all live pretty much in the same package, so it'd be easy to squash them down before merging to main, if we want to move this to a separate tool in the future.