[keyserver] Add special_role column in migration 52

Summary:
For those who incrementally went from migration 50 --> 52 --> 56 (or any number after 52), all of the migrations should have succeeded since the updateRolesAndPermissionsForAllThreads migration would have been run on queries that used threads.default_role, not roles.special_role.

However, following some new code in this stack, we updated the queries to use the special_role field.

For those who did not update their migration version incrementally and attempted to go from an older version like 50 straight to 56, the updateRolesAndPermissionsForAllThreads would fail because the queries attempt to fetch a roles.special_role columm, but that doesn't yet exist in their database state.

Here, we prefix migration 52 with the ALTER TABLE statement so we can add in a special_role column before the updateRolesAndPermissionsForAllThreads so the user's DB state has it before attempting to run any queries with it

Addresses ENG-5999

Test Plan:
Ran the following queries to 'reset' what my DB would have looked like from migration 50:

ALTER TABLE threads ADD COLUMN default_role bigint(20) NOT NULL;
ALTER TABLE invite_links DROP COLUMN blob_holder;
ALTER TABLE roles DROP COLUMN special_role;

Following that, attempting to start up keyserver resulted in the same error as ENG-5999.

(node:90468) DB version: 50
(node:90468) migration 51 succeeded.
recalculating permissions for threads with depth 0
updating roles for 1
updating roles for 83880
updating roles for 83894
updating roles for 83903
updating roles for 83912
updating roles for 83961
(node:90468) migration 52 failed.
Unknown column 'special_role' in 'field list'
[nodemon] app crashed - waiting for file changes before starting...

After making these changes, I attempted to start up keyserver again and saw the migrations succeeded

Reviewers: ashoat, ginsu, atul

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D10132