[keyserver] Recalculate permissions and reintroduce ADD_MEMBERS permission

Summary:
This diff does two things:

1. Resolves ENG-9055 by bringing back ADD_MEMBERS permissions. Unfortunately we have no way to determine which communities had this permission before the errant migration, so I'm just assuming they all had it (as it's a default) and bringing it back for all communities.
2. Recalculates all permissions so that the changes in the last two diffs in the stack are applied.

Depends on D13113

Test Plan:

1. I set up a repro of ENG-9055 in my local environment
2. I confirmed that after this migration ran, ADD_MEMBERS permission was present

Reviewers: tomek, inka

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D13114