Adds new suite of metrics to capture the following for capnp rpcs operations:
- Method calls
- Method call failures
- Method call latencies
Each of the operations is labeled by the handler that serves the method and
the method of operation invoked. Additionally, each of these are split
between if the operation was called by a client or served.
For Google's managed prometheus, it seems they reserved certain
labels for their internal service regions/locations. This causes
customers to run into issues using our metrics since our
metric: `cloudflared_tunnel_server_locations` has a `location`
label. Renaming this to `edge_location` should unblock the
conflict and usage.
Devin Carr
João Oliveirinha
Igor Postelnik
Areg Harutyunyan
cthuang