+ akka-cluster-metrics: new akka module

* new akka module split from akka-cluster
* provides sigar provisioning
* resolve #16121
* see #16354
removed

-------- Original Message --------
In akka-cluster-metrics/src/main/resources/reference.conf
<https://github.com/akka/akka/pull/16475#discussion-diff-21667017>:
> > +            # Configuration of the default strategy provider.
> > +            # Replace with custom settings when overriding the provider.
> > +            configuration = {
> > +                # Log restart attempts.
> > +                loggingEnabled = true
> > +                # Child actor restart-on-failure window.
> > +                withinTimeRange = 3s
> > +                # Maximum number of restart attempts before child actor is stopped.
> > +                maxNrOfRetries = 3
> > +            }
> > +        }
> > +    }
> > +    # Metrics collector actor.
> > +    collector {
> > +        # Actor name. Example name space: /system/cluster-metrics/collector
> > +        name = "collector"
>
> why would the user need to change the name?
>
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> <https://github.com/akka/akka/pull/16475/files#r21667017>.
>