Add telemetry measurements to key functionality

[jrasell]

Is your feature request related to a problem? Please describe.
Sherpa currently ships with the ability to send metrics to a number of backends, however, the current metrics that are emitted are only the default runtime metrics from Go. It would aid operators to have further metrics which provides greater insight to the server health and actions which have been taken.

Initial thoughts on where to implement:

• storage backend call times
• scale in/out success failure counts
• autoscaler run time