Does the host labels: _hostname=!* solution mean something like

host labels: _hostname=!*

translate to a go.d/postgres.conf file that looks like

jobs:
  - name: local
    dsn: 'host=/var/run/postgresql dbname={{ seasensor_database_name }}  user=netdata'
    timeout: 4
host:
  labels: _hostname=!*

and if so how would this match specifically to postgres_db_cache_io_ratio without disabling other alarms in the module?

Does the host labels: _hostname=!* solution mean something like

Yes. But you need to add this line to the alert you want to disable.

Or

1. Open netdata.conf.
2. Go to [health].
3. Uncomment and update enabled alarms = !postgres_db_cache_io_ratio *.
4. Restart netdata service.