Prometheus integration

This integration exposes metrics in a Prometheus compatible format.

Metric naming guidelines

Please follow these guidelines while defining metrics.

• Metric and label names should conform to Prometheus naming guidelines.
• Domain-specific metrics should have the domain (sensor, switch, climate, etc.) as a metric name prefix.
• Enum-like values (e.g. entity state or current mode) should be exported using a "boolean" metric (values of 0 or 1) broken down by state/mode (as a metric label).