* add metrics and tracing to state manager
* propagate tracer to state manager
* add scheduler metrics
* fix backtesting
* add test for state metrics
* remove StateUpdateCount
* update docs
* metrics can be null
* add tracer to new tests
The `rule_groups_rules` metric is currently defined and computed by `State`.
It makes more sense for this metric to be computed off of the configured rule
set, not based on the rule evaluation state. There could be an edge condition
where a rule does not have a state yet, and so is uncounted.
Additionally, we would like this metric (and others), to have a `rule_group`
label, and this is much easier to achieve if the metric is produced from the
`Scheduler` package.
