Support Postgres materialized views

[rubenhelsloot]

Describe the bug
I want to compare two materialized views built using DBT, but when I run data-diff --dbt --select <my model>, I get "New model or no access to prod table." The reason is that is that in Postgres, materialized views are not stored in the information_schema.columns schema, which is what is queried by data-diff to find the column:

SELECT column_name, data_type, datetime_precision,                                                                                 
    -- see comment for DEFAULT_NUMERIC_PRECISION                                                                   
    CASE                                                                                                           
        WHEN data_type = 'numeric'                                                                                 
            THEN coalesce(numeric_precision, 131072 + 16383)                                                       
        ELSE numeric_precision                                                                                     
    END AS numeric_precision,                                                                                      
    CASE                                                                                                           
        WHEN data_type = 'numeric'                                                                                 
            THEN coalesce(numeric_scale, 16383)                                                                    
        ELSE numeric_scale                                                                                         
    END AS numeric_scale                                                                                           
    FROM information_schema.columns
    WHERE table_name = '<my model>' AND table_schema = 'intermediate_prod'

Instead, we'd need to query pg_matviews, as noted in this StackOverflow answer.

I figure we could solve this issue by unioning the first query with another one that queries pg_matviews.

Describe the environment
I'm running data-diff v0.11.0 with dbt-core and dbt-postgres 1.7.7 on Postgres 15.

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