R1:763b63a0fb81

Add spacePHID infrastructure and implement in Paste

Summary:
Ref T8424. I'm using Paste as a testbed application because Spaces make some degree of sense for it but it's also flat/simple.

This doesn't do anything interesting or useful and mostly just making the next (more interesting) diff smaller.

Test Plan:
- Ran `bin/storage upgrade -f`.
- Browsed pastes.
- Created a paste.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8424

Differential Revision: https…