Return value of search_type in /config/type API endpoint

- Remove need for interfaces to downcase content types returned by API
  before using the type in search and other API endpoint
- Fix to check for search_type.name in plugin keys instead of value

src/khoj/interface/web/index.html

@@ -65,7 +65,7 @@
         function search(rerank=false) {
             // Extract required fields for search from form
             query = document.getElementById("query").value.trim();
-            type = document.getElementById("type").value.toLowerCase();
+            type = document.getElementById("type").value;
             results_count = document.getElementById("results-count").value || 6;
             console.log(`Query: ${query}, Type: ${type}`);