[Keyserver] Apply DB Migrations

Summary:
Ensure that the user_credentials are available, and allow
for the metadata table to hold a 512 character long access token.

Depends on D8399

Test Plan:

yarn dev

Reviewers: ashoat, kamil, michal

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8400