Implement "unsaved mod defintions" with @inner registry IDs - Slice 2

[BLoe]

• Change the Add button to New Mod
• Temporary, "unsaved" mod metadata added to the new component, with id as @inner/mod/<uuid>
  • Don't use the component id as part of the mod id, generate a new uuid, because the component could be moved around and used to create new mods multiple times, and we don't want id collision

Acceptance Criteria

1. I click Add/New dropdown
2. I select a starter brick
3. I see a unsaved mod definition with the starter brick
4. I add a pipeline to the starter brick
5. I click the save button (because of slice 1, this only exists at the mod-level)
6. I see the Save Mod modal
7. I do not see @inner/mod/<uuid> as the mod id
8. I see @<my-scope>/.... with the scope dropdown, etc.
9. I click the save button in the create mod modal