Add Migrations Table to Tokenserver envs

We currently default to disabling db migrations in Tokenserver (SYNC_TOKENSERVER__RUN_MIGRATIONS=false) as the migrations were only created for the Rust rewrite and we already had pre-existing databases in our prod/etc. environments.

Ideally we would switch this to default to true: to do this safely we should add the diesel migrations table to these environments (as if the migrations had already been ran, basically the __diesel_schema_migrations table), which would let us safely enable migrations on these environments in the future.

This would enable the use of migrations on our prod/etc. environments in the future and improve the default setting for other environments (such as self hosters, enterprise).

┆Issue is synchronized with this Jira Task

Start by locating the Tokenserver environment configuration that sets SYNC_TOKENSERVER__RUN_MIGRATIONS and identifying the prod and other environments covered by this task. Verify how the __diesel_schema_migrations table should be introduced without applying existing migrations; done means the listed environments contain the table and can safely enable migrations later.