Network version Prometheus metric

[LesnyRumcajs]

Summary

To facilitate infrastructure operations, Forest should expose a Prometheus metric with the network version. Note that not all cases will be caught by it, given some network versions might be duplicated due to fixes:

            Height::Thunder => NetworkVersion::V20,
            Height::Watermelon => NetworkVersion::V21,
            Height::WatermelonFix => NetworkVersion::V21,
            Height::WatermelonFix2 => NetworkVersion::V21,
            Height::Dragon => NetworkVersion::V22,
            Height::DragonFix => NetworkVersion::V22,
            Height::Phoenix => NetworkVersion::V22,

Completion Criteria

• expose network version as a Prometheus metric
• include the metric in https://github.com/ChainSafe/forest/tree/main/monitoring

Additional Links & Resources

[LesnyRumcajs]

cc @joshdougall