Make interpretation location a variable

We're adding inline interpretations to Regulation D. Unlike all of our other
regs, Reg D houses its interpretations in Appendix A instead of Supplement I.
We had "Supplement I" hardcoded into the text of the links at the end of all
inline interpretations, which didn't make sense for inline interps in Reg D.
This commit fixes that by making the reference to the location of the interps
in those links a variable and sets up a special case for Reg D interps.

cfgov/regulations3k/jinja2/regulations3k/inline_interps.html

@@ -1,3 +1,6 @@
+{#- Part 1004 (Reg D) houses interps in Appendix A instead of Supplement I like every other reg -#}
+{%- set interp_location = 'Appendix A' if regulation and regulation.part_number == '1004' else 'Supplement I' -%}
+
 <div data-qa-hook="expandable"
      class="o-expandable
             o-expandable__padded
@@ -28,7 +31,7 @@
     <div class="o-expandable_content">
         {{ contents }}
 
-        <p><a href="{{ url }}">See interpretation of {% if section_title %}{{ section_title }}{% else %}this section{% endif %} in Supplement I</a></p>
+        <p><a href="{{ url }}">See interpretation of {% if section_title %}{{ section_title }}{% else %}this section{% endif %} in {{ interp_location }}</a></p>
     </div>
 
 </div>