Escape % symbols in table/view/column comments (#466) (#471)

* Use tests with table/view/column-level comments

* Changelog entry

* escape % until the underlying issue is fixed in redshift_connector

* Revert "Use tests with table/view/column-level comments"

This reverts commit 1b41d8c.

(cherry picked from commit adb4482)

Co-authored-by: Doug Beatty <44704949+dbeatty10@users.noreply.github.com>

.changes/unreleased/Fixes-20230524-151825.yaml

@@ -0,0 +1,6 @@
+kind: Fixes
+body: Escape `%` symbols in table/view/column comments
+time: 2023-05-24T15:18:25.834088-06:00
+custom:
+  Author: dbeatty10
+  Issue: "441"

dbt/include/redshift/macros/adapters.sql

@@ -292,3 +292,21 @@
   {% endif %}
 
 {% endmacro %}
+
+{#
+  By using dollar-quoting like this, users can embed anything they want into their comments
+  (including nested dollar-quoting), as long as they do not use this exact dollar-quoting
+  label. It would be nice to just pick a new one but eventually you do have to give up.
+#}
+{% macro postgres_escape_comment(comment) -%}
+  {% if comment is not string %}
+    {% do exceptions.raise_compiler_error('cannot escape a non-string: ' ~ comment) %}
+  {% endif %}
+  {%- set magic = '$dbt_comment_literal_block$' -%}
+  {%- if magic in comment -%}
+    {%- do exceptions.raise_compiler_error('The string ' ~ magic ~ ' is not allowed in comments.') -%}
+  {%- endif -%}
+  {#- -- escape % until the underlying issue is fixed in redshift_connector -#}
+  {%- set comment = comment|replace("%", "%%") -%}
+  {{ magic }}{{ comment }}{{ magic }}
+{%- endmacro %}