Sets `http.Server.IdleTimeout` and `http.Client.IdleConnTimeout`
on clients and servers which didn't have them set. A default of
360s was chosen to be on par with the default of an NLB without
being identical.
This was added as another safety measure to prevent leaking any
idle connections indefinitely as seen in #22757.
`apidefaults.DefaultDialTimeout` was also renamed to
`apidefaults.DefaultIOTimeout` to better reflect its usage.
rosstimothy
c2fc9a9375