feat(model-team): simplify objectId and objectType storage

BREAKING CHANGE: Previously objectId and objectType were stored in a JSONB column on the teams
table. This has changed (and the migration takes care of table and data migration) in favor of
storing objectId and objectType as flat columns on the teams table. For reasons of querying,
indexing and ease of use, this is a better option. The read side of the API still returns a nested
TeamObject, but the GraphQL mutations have changed (see `team_graphql_test.js` for some examples).