Add dbug_flag namelist setting

Previously this could only be set via a code change

Author: billsacks

cime_config/namelist_definition_drv.xml

@@ -879,6 +879,30 @@
     </values>
   </entry>
 
+  <entry id="dbug_flag">
+    <type>integer</type>
+    <category>expdef</category>
+    <group>MED_attributes</group>
+    <desc>
+      Level of debug output; higher values give progressively more output
+
+      Some example values (other values are also accepted)
+      - 0: no extra debug output
+      - 1: a bit of debug output
+      - 2: a bit more debug output
+      - 6: a moderate amount of debug output
+      - 11: a lot of debug output
+      - 21: a huge amount of debug output
+
+      Note that setting this to moderate - high values can lead to overwhelming amounts of output.
+
+      (Default: 0)
+    </desc>
+    <values>
+      <value>0</value>
+    </values>
+  </entry>
+
   <entry id="flux_albav" modify_via_xml="CPL_ALBAV">
     <type>logical</type>
     <category>control</category>