Prefix lh_ on Prometheus Metrics for lh-server

[mijailr]

I would like to request the addition of a lh_ prefix to all Prometheus metrics exposed by the lh-server. This change can improve the clarity and uniformity of metrics, especially when integrating with other systems or when multiple services expose metrics to the same Prometheus instance.

[coltmcnealy-lh]

This would be a breaking change. Adding it to the 1.0 milestone.

[coltmcnealy-lh]

Actually, after 5 seconds more thought, we could do this through a configuration: LHS_METRICS_PREFIX. It could default to the empty string. Operators of LittleHorse could opt-in to lh_ if they want. That would be the most flexible and best approach, and it wouldn't require a breaking change. Removing from the milestone (with apologies to our Grumpy Maintainer for the chaos).