Add Rollgate to Tools

[tech-and-finance]

Adds Rollgate to the Tools section.

Rollgate is a feature flag management platform that fits the GitOps workflow alongside CloudBees Rollout (already listed). Key features relevant to GitOps practitioners:

• Scheduled flag changes — Program flag activations for specific dates/times, auditable and reviewable
• Instant rollback — Full state snapshots with 1-click restore to any previous flag configuration
• Gradual rollouts — Percentage-based using consistent hashing (MurmurHash3), so the same user always sees the same variant across deploys
• JSON-based flag config — Exportable flag state works well with Git-based review workflows
• Real-time updates via SSE — Connected clients see flag changes within seconds, no polling required
• 13 open-source SDKs — Go, Node, Python, Java, .NET, Flutter, React, Vue, Angular, Svelte, React Native, Browser (https://github.com/rollgate/sdks)

Free tier includes 500K API requests/month, 3 projects, unlimited flags, and all SDKs.