Implement support for user-configurable script export locations

[deviaze]

Adds an easy way to change the auto-export location by clicking an instance in Explorer then clicking the relevant "Change Parent" button for either Client, Server, or Tooling.

• Output locations are now displayed with actual Roblox paths (like Client Export Location: ReplicatedStorage["ZapClient"]) so users know exactly where their scripts are going.
• Every time a user changes their Roblox Studio selection, starts typing in Zappy plugin textboxes, or clicks a "Change Parent" button, the rest of the Zappy UI updates. This makes it really responsive to change settings and figure out where scripts will get exported.
• Made major changes to the plugin's UI and src/Zappy/init.server.luau to accommodate the new functionality.
• The new Client Output/Server Output/Tooling Output sections can each be individually collapsed and are nested under a parent VerticalCollapsibleSection named Output Settings.
• Client/Server/Tooling buttons are color-coded for sanity and don't take up the whole X-axis to visually distinguish them from the Generate button.
• Uses CollectionService tags under the hood to keep track of state and save output location instances between Studio sessions.
• Updated README.md to showcase the new UI and how to use it.

The new UI with the new menus expanded looks like: