Investigate if we can add metrics for HTTP ReadHeaderTimeout for Workhorse

The following discussion from !179305 (merged) should be addressed:

• @ashmckenzie started a discussion:

Let's see. From https://ieftimov.com/posts/make-resilient-golang-net-http-servers-using-timeouts-deadlines-context-cancellation/, I see:

I got confused between ReadTimeout and ReadHeaderTimeout. Setting a 90-second ReadTimeout had me much more concerned. https://pkg.go.dev/net/http says this:

	// ReadHeaderTimeout is the amount of time allowed to read
	// request headers. The connection's read deadline is reset
	// after reading the headers and the Handler can decide what
	// is considered too slow for the body. If zero, the value of
	// ReadTimeout is used. If negative, or if zero and ReadTimeout
	// is zero or negative, there is no timeout.
	ReadHeaderTimeout time.Duration

Yeah, I think 90 seconds should be more than enough. I wish we'd be able to see these metrics to get a better idea where we are today.