Query table_comments without unrolling with UNION ALL

`table_comments` is equally "hard" for the engine as
`information_schema.columns`. Avoid optimizing the query on the `dbt`
side by sending `UNION ALL` with individual schemas. Let the engine
figure out the optimal strategy.

.changes/unreleased/Under the Hood-20231003-161428.yaml

@@ -0,0 +1,7 @@
+kind: Under the Hood
+body: Query table_comments without unrolling with UNION ALL
+time: 2023-10-03T16:14:28.238801+02:00
+custom:
+  Author: findepi
+  Issue: ""
+  PR: "357"

dbt/include/trino/macros/catalog.sql

@@ -38,7 +38,6 @@
         ),
 
         table_comment as (
-            {%- for schema in schemas %}
             select
                 catalog_name as "table_database",
                 schema_name as "table_schema",
@@ -51,11 +50,7 @@
                 and
                 schema_name != 'information_schema'
                 and
-                schema_name = '{{ schema | lower }}'
-            {% if not loop.last %}
-            union all
-            {% endif %}
-            {%- endfor %}
+                table_schema in ('{{ schemas | join("','") | lower }}')
         )
 
         select