R1:adde4089b49b

Allow owners paths to be arbitrarily long and add storage for display paths

Summary:
Depends on D19182. Ref T11015. This changes `path` from `text255` to `longtext` because paths may be arbitrarily long.

It adds `pathDisplay` to prepare for display paths and storage paths having different values. For now, `pathDisplay` is copied from `path` and always has the same value.

Test Plan:
- Ran migration, checked database for sanity (all `pathDisplay` and `path` values identical).
- Added new paths, saw…