Add ADR type to search page and result cast

Signed-off-by: Stephen Cprek <steve.cprek@favordelivery.com>

plugins/adr/README.md

@@ -71,16 +71,32 @@ Afterwards, add the following code snippet to use `AdrSearchResultListItem` when
 import { AdrSearchResultListItem } from '@backstage/plugin-adr';
 
 ...
+<SearchType.Accordion
+  name="Result Type"
+  defaultValue="software-catalog"
+  types={[
+    ...
+    {
+      value: 'adrs',
+      name: 'Architecture Decision Records',
+      icon: <DocsIcon />,
+    },
+  ]}
+/>
 
-case 'adr':
+...
+
+case 'adrs':
   return (
     <AdrSearchResultListItem
       key={document.location}
-      result={document}
+      result={document as AdrDocument}
     />
   );
 ```
 
+> Note the `AdrDocument` might not be needed in newer versions https://github.com/backstage/backstage/issues/13723
+
 ## Custom ADR formats
 
 By default, this plugin will parse ADRs according to the format specified by the [Markdown Architecture Decision Record (MADR) v2.x template](https://github.com/adr/madr/tree/2.1.2). If your ADRs are written using a different format, you can apply the following customizations to correctly identify and parse your documents: