Use content negotiation hint to identify requests

Allow the server to reply with a response body unique to remote-input
requests by sending an Accept header hint in the request. A partial HTML
fragment might be returned rather than a full page.

Author: dgraham

index.js

@@ -71,7 +71,7 @@ async function fetchResults(remoteInput: RemoteInputElement, checkCurrentQuery:
   remoteInput.dispatchEvent(new CustomEvent('loadstart'))
   remoteInput.setAttribute('loading', '')
   try {
-    const response = await fetch(url)
+    const response = await fetch(url, {headers: {accept: 'text/html; fragment'}})
     const html = await response.text()
     remoteInput.dispatchEvent(new CustomEvent('load'))
     resultsContainer.innerHTML = html