refactor: update tracker label convention from z_campain_<id>

[mnkiefer]

• Refactors old label format campaign:<campaignId> to z_campaign_<campaignId> (to place it at the bottom of labels, not as discoverable/in the way).
• Also updates the campaign discovery logic to simplify GitHub search queries by removing unnecessary parentheses, and adjusts related tests to ensure correct query formatting.

[mnkiefer]

@copilot Check if this fixes 0 discovery items we've been seeing.

[Copilot]

@mnkiefer I've opened a new pull request, #11472, to work on those changes. Once the pull request is ready, I'll request review from you.