Add Prometheus metrics

src/firehose.ts

@@ -1,5 +1,6 @@
 import { Stickynotes } from '@soapbox/stickynotes';
 
+import { firehoseEventCounter } from '@/metrics.ts';
 import { Storages } from '@/storages.ts';
 import { nostrNow } from '@/utils.ts';
 
@@ -12,13 +13,14 @@ const console = new Stickynotes('ditto:firehose');
  * side-effects based on them, such as trending hashtag tracking
  * and storing events for notifications and the home feed.
  */
-export async function startFirehose() {
+export async function startFirehose(): Promise<void> {
   const store = await Storages.client();
 
   for await (const msg of store.req([{ kinds: [0, 1, 3, 5, 6, 7, 9735, 10002], limit: 0, since: nostrNow() }])) {
     if (msg[0] === 'EVENT') {
       const event = msg[2];
       console.debug(`NostrEvent<${event.kind}> ${event.id}`);
+      firehoseEventCounter.inc({ kind: event.kind });
 
       pipeline
         .handleEvent(event, AbortSignal.timeout(5000))