Turned on feature flag metric

[KaloyanTanev]

🎯 Problem to be solved

Recently we are using feature flags more extensively.
One bummer with them is that it's hard to judge what feature flags a node has turned on. Some of them might be incompatible with other feature flags, new stable features, upcoming forks, different VC/BN versions, etc.

🛠️ Proposed solution

• Add a metric to prometheus that keeps track of enabled feature flags on node start.

🧪 Tests

• Metric is visible in Grafana