Drop dependent caggs materialized views.

[rapito]

Description

This PR fetches all caggs view dependencies of a table before deleting it to drop those first and avoid a potential dependency error that is not solved automatically by force: :cascade

Changes

• Added helper method to schema_statements to fetch dependent views and execute drop materialized view on them.
• Added drop_table to schema_statements and called the helper mentioned above.
• Updated create_table to schema_statements and called the helper mentioned above.
• Updated specs.

Context

When there are nested or dependent caggregations and create_table or drop_table are invoked with force: :cascade an error is raised indicating that the object cannot be deleted because another one depends on it.

This does not occur if a hyptertable has a single caggregation. But it does occur if you add a second layer and introduce another caggregation to the first one.

i.e:

1. create table with hypertable option
2. create a cagg with time_bucket of 1 hour on that table, named events_per_hour
3. create another cagg with time_bucket of 1 day on events_per_day

You can see the behaviour by running this gist, or on the tests.

This causes that a migration that tries to override a table with such configuration fails.
Also, trying to run schema:load twice fails. (for whatever reason someone would need or want to do this)