Remove use of JSONB columns

[awrichar]

A few of the database tables are currently using JSONB columns, which incur the overhead of parsing
and indexing the JSON contents. These can be replaced with BYTEA since we do not require this
indexing.

[peterbroadhurst]

I note I think it's fine just to change the existing migrations that create the tables, rather than introducing complex migrations that change the types of existing created tables.