chore: increase contact announcement interval

[CassOnMars]

Why is this change needed?

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

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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

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Name	Status	Preview	Comments	Updated (UTC)
hub-monorepo	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Sep 6, 2024 1:44am

[changeset-bot]

🦋 Changeset detected

Latest commit: 2c708cf

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@farcaster/hubble	Patch

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