Populate Postgres description fields

[pjonsson]

After running datacube system init with the postgis driver, this is how things show up in psql:

datacube=# \du+
                                     List of roles
 Role name  |                         Attributes                         | Description
------------+------------------------------------------------------------+-------------
 odc_admin  | Create role, Cannot login                                  |
 odc_manage | Cannot login                                               |
 odc_user   | Cannot login                                               |
 postgres   | Superuser, Create role, Create DB, Replication, Bypass RLS |

datacube=# \dn+
                                       List of schemas
  Name  |       Owner       |           Access privileges            |      Description
--------+-------------------+----------------------------------------+------------------------
 odc    | odc_admin         | odc_admin=UC/odc_admin                +|
        |                   | odc_user=U/odc_admin                  +|
        |                   | odc_manage=C/odc_admin                 |
 public | pg_database_owner | pg_database_owner=UC/pg_database_owner+| standard public schema
        |                   | =U/pg_database_owner                   |
(2 rows)

I think it would be nice if the description fields were populated with a brief description instead of left empty.