Fixes #641 by using the svv_mv_info view which is queryable

[reptillicus]

resolves #641

Problem

When doing a dbt run on a redshift serverless cluster, permission denied errors will happen when dbt attempts to query the svt_mv_info table. This is due to that table not being queryable by any user in redshift serverless as described here.

Solution

This can be remedied by a custom macro for redshift__describe_materialized_view, which references the svv_mv_info view instead of the svt_mv_info table as shown below

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) or this PR has already received feedback and approval from Product or DX

[reptillicus]

@dbeatty10 here's a wee little PR

[colin-rogers-dbt]

@jiezhen-chen any reason we shouldn't use svv_mv_info?

[mikealfare]

@jiezhen-chen any reason we shouldn't use svv_mv_info?

In particular, is there a reason to use svv_mv_info over stv_mv_info or vice versa? We want to make sure we're not trading one problem for another. On the surface these seem like very similar objects. I'd also like to stick a comment somewhere that explains why we're using one over the other so we don't accidentally revert this in the future.