resolves #9419

Problem

As described in #9419 (comment), the information_schema.columns view in postgres includes these:

• o[r]dinary table, [v]iew, [f]oreign table, [p]artitioned table

But it does not include:

• [m]aterialized view

Solution

Two things:

1. 531446e Add the full definition of the information_schema.columns view into dbt-postgres.
2. afaca63 Add 'm'::"char" to the definition so that MVs are included.

Definition of the information_schema.columns view

To get the full text definition of this view, run the following:

select definition 
from pg_catalog.pg_views 
where schemaname = 'information_schema' 
  and viewname = 'columns'

The output is a fairly gnarly query as seen in 531446e

To do

After a quick search, I couldn't find any relevant tests for adapter.get_columns_in_relation, so we'll probably want some that cover all the different types of relations:

• ephemeral
• table
• view
• materialized view

The tests would basically just need to:

1. Define a relation with a column or two.
2. Build it.
3. Make sure that those columns are returned by adapter.get_columns_in_relation.

I'm assuming that ephemeral will either raise an exception or return nothing, but we'll want to add applicable tests either way.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• 👈 This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc)