chore: increase contact announcement interval (#2296)

## Why is this change needed?

Reduces the interval from every 30 to every 15 minutes for announcement,
with randomized start minute

## Merge Checklist

_Choose all relevant options below by adding an `x` now or at any time
before submitting for review_

- [x] PR title adheres to the [conventional
commits](https://www.conventionalcommits.org/en/v1.0.0/) standard
- [x] PR has a
[changeset](https://github.com/farcasterxyz/hub-monorepo/blob/main/CONTRIBUTING.md#35-adding-changesets)
- [x] PR has been tagged with a change label(s) (i.e. documentation,
feature, bugfix, or chore)
- [ ] PR includes
[documentation](https://github.com/farcasterxyz/hub-monorepo/blob/main/CONTRIBUTING.md#32-writing-docs)
if necessary.

<!-- start pr-codex -->

---

## PR-Codex overview
This PR adjusts the announcement interval for contact info in the
`@farcaster/hubble` package.

### Detailed summary
- Changed the random minute calculation from every 30 minutes to every
15 minutes in `hubble.ts`
- Updated the cron syntax for `gossipContactInfoJobScheduler` to reflect
the new interval

> ✨ Ask PR-Codex anything about this PR by commenting with `/codex {your
question}`

<!-- end pr-codex -->

.changeset/angry-fans-search.md

@@ -0,0 +1,5 @@
+---
+"@farcaster/hubble": patch
+---
+
+chore: adjust announcement interval for contact info

apps/hubble/src/hubble.ts

@@ -821,8 +821,8 @@ export class Hub implements HubInterface {
     this.checkFarcasterVersionJobScheduler.start();
     this.validateOrRevokeMessagesJobScheduler.start();
 
-    const randomMinute = Math.floor(Math.random() * 30);
-    this.gossipContactInfoJobScheduler.start(`${randomMinute} */30 * * * *`); // Random minute every 30 minutes
+    const randomMinute = Math.floor(Math.random() * 15);
+    this.gossipContactInfoJobScheduler.start(`${randomMinute}-59/15 * * * *`); // Weird syntax but required by cron, random minute every 15 minutes
     this.checkIncomingPortsJobScheduler.start();
     this.measureSyncHealthJobScheduler.start();