[CT-1519] Adding friendlier error message when dist is improperly set as a list or mapping

.changes/unreleased/Fixes-20221122-172014.yaml

@@ -0,0 +1,7 @@
+kind: Fixes
+body: Friendlier error message for misspecified distkey type
+time: 2022-11-22T17:20:14.432522-08:00
+custom:
+  Author: dluftspring
+  Issue: "224"
+  PR: "226"

dbt/include/redshift/macros/adapters.sql

@@ -1,6 +1,10 @@
 
 {% macro dist(dist) %}
   {%- if dist is not none -%}
+      {%- if dist is iterable or dist is mapping -%}
+        {% exceptions.raise_compiler_error("Expected a single valued property for dist and got: " ~ dist ~ " instead") %}
+      {%- endif -%}
+
       {%- set dist = dist.strip().lower() -%}
 
       {%- if dist in ['all', 'even'] -%}