Support additional timings in COMMON_DURATION

[guydc]

Description:
Envoy currently records several upstream connection time points that are not supported by the %COMMON_DURATION(...)% operator:

envoy/envoy/stream_info/stream_info.h

Lines 352 to 354 in 2c84739

	absl::optional<MonotonicTime> upstream_connect_start_;
	absl::optional<MonotonicTime> upstream_connect_complete_;
	absl::optional<MonotonicTime> upstream_handshake_complete_;

These timestamps are useful for identifying the overhead of upstream TCP/TLS connection establishment. The %UPSTREAM_CONNECTION_POOL_READY_DURATION% operator provides the total connection establishment time, but it does not distinguish between the TCP and TLS parts and is only available in millisecond resolution. The above-mentioned time points can be supported in the %COMMON_DURATION(...)% operator to achieve that.