fix(instrumented_http): migrate to own http instrumenter

[ivankatliarchuk]

What does it do ?

• No more warning "Warning: unable to cancel request" roundTripperType="*instrumented_http.Transport"
• The code https://github.com/linki/instrumented_http moved under external-dns umbrella. Slighly simpliefied, as not everything is required.
• The issue is, RoundTripper use to have a method CancelRequest(). But it was deprecated for quite a while net/http: make Transport.CancelRequest somehow work against http2 golang/go#14095 and x/net/http2: decide what to do about Transport.CancelRequest golang/go#13540 and was removed few versions ago while some clients still attempt to use it via type assertion.
• Relevant upstream code that triggers the warning: https://github.com/kubernetes/client-go/blob/master/transport/transport.go#L346-L358. It's actually an info. The source of the issue is that RoundTripper does not implement CancelRequest.

Owning this code, will let us to instrument more metrics, for example we could add TLS handshakes or DNS resolution latencies, to further improve operational experience.

trace := &promhttp.InstrumentTrace{
	DNSStart: func(t float64) {
		dnsLatencyVec.WithLabelValues("dns_start").Observe(t)
	},
	DNSDone: func(t float64) {
		dnsLatencyVec.WithLabelValues("dns_done").Observe(t)
	},
	TLSHandshakeStart: func(t float64) {
		tlsLatencyVec.WithLabelValues("tls_handshake_start").Observe(t)
	},
	TLSHandshakeDone: func(t float64) {
		tlsLatencyVec.WithLabelValues("tls_handshake_done").Observe(t)
	},
}

Motivation

Fixes #5140

before, just enourmous amount of warning logs

with the fix

Tested. Metrics looks exactly same

Namespace external_dns not added, to keep it as is

http_request_duration_seconds
http_request_duration_seconds_sum

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

[AndrewCharlesHay]

/lgtm

[Raffo]

Big fan of removing that old dependency, we should have done it earlier.

/lgtm

[ivankatliarchuk]

/approve

[k8s-ci-robot]

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