Log DNS resolution times when debug http is enabled

[patrobinson]

We print the time when a request starts and a response is received, but this also includes any DNS resolution.
To help debug slow DNS issues this PR now prints the timings when it starts/stops.

Inspired by golang/go#21906 (comment)

Output:

dns start: 2024-05-03 17:25:37.519031 +1000 AEST m=+0.013530292
dns done: 2024-05-03 17:25:37.556161 +1000 AEST m=+0.050660126
connection start: 2024-05-03 17:25:37.556272 +1000 AEST m=+0.050770667
connection done: 2024-05-03 17:25:37.708357 +1000 AEST m=+0.202855251
TLS Handshake start: 2024-05-03 17:25:37.70846 +1000 AEST m=+0.202958042
TLS Handshake done: 2024-05-03 17:25:37.872324 +1000 AEST m=+0.366821292
wrote headers: 2024-05-03 17:25:37.872614 +1000 AEST m=+0.367111959
wrote request: 2024-05-03 17:25:37.87262 +1000 AEST m=+0.367117334