* Instrument proxy frontend latency metric
Backend latency only captures the time spent waiting for the GAE backend
to respond to a request, which is not representitive of what clients
experience. For instance it does not take into account the time the
proxy spends on processing the requests and the time it takes to send a
response to the client.
This PR adds a metric for frontend latency, which is the time spent on
answering a client request. This should serve as a better proxy for the
latency clients observe.
* Rename AbstractMetrics to BaseMetrics
https://github.com/google/nomulus/pull/129 migrated `GoogleCredential`
to `GoogleCredentialsBundle` and introduced a subtle bug. I don't fully
understand why but there are times when the access token is null but
`credentials.refresh()` is not called, resulting in NullPointerException
when `credentials.getAccessToken().getTokenValue()` is called.
Since the new GoogleCredentials class supports `shouldRefresh()`, we now
just rely on it to make sure that we always get a value access token.
Replace deprecated GoogleCredential with new lib
This PR also introduced a CredentialsBundle class to carry
HttpTransport and JsonFactory object which are needed by
most of the GCP library to instantiate client.
* Move terraform and kubernetes folder to be under proxy
There is no reason for them to be under proxy/src/... any more now that
we have a Gradle-idiomatic folder structure.
