Improve Postgresql adapter when using Apartment.use_sql and Apartment.use_schemas

[NielsKSchjoedt]

• Fix: Remove CREATE SCHEMA clause for default_schema from structure dump definition.
• Improve: The structure dump now points foreign key constrains that references excluded_models to default_schema instead of the new schema.

_An example_

With a config like this:

Apartment.configure do |config|
  config.excluded_models = ["User"]
  config.use_schemas = true
  config.use_sql = true
  config.persistent_schemas = ['extensions']
  config.default_schema = 'da'
  config.tenant_names = ['da', 'se', 'us']
end

The definitions will now look like this:

ALTER TABLE ONLY feedbacks
    ADD CONSTRAINT feedbacks_user_id_fk FOREIGN KEY (user_id) REFERENCES da.users(id) ON DELETE CASCADE;

Instead of this:

ALTER TABLE ONLY feedbacks
    ADD CONSTRAINT feedbacks_user_id_fk FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;

[mikecmpbll]

why doesn't pg_dump dump foreign key constraints that reference other schemas properly? and why does it include a definition for the default schema?

apologies if they're silly questions, i'm not that familiar with pg yet :).