[connector/spanmetrics] spanmetrics connector do not attach exemplar any more

[fatsheep9146]

Component(s)

connector/spanmetrics

What happened?

Description

After using spanmetrics connector instead of spanmetrics processor, I found that exemplar info are no longer attached to metrics.

I tried to dig and find the possible root cause is

opentelemetry-collector-contrib/connector/spanmetricsconnector/internal/metrics/metrics.go

Lines 113 to 114 in 3dc9d21

	for i := 0; i < dp.Exemplars().Len(); i++ {
	dp.Exemplars().At(i).SetTimestamp(timestamp)

and I already tried to fix it and send a pr. Please correct me if I do it wrong.

Steps to Reproduce

Just use the basic usage of spanmetrics connector and use prometheus receiver, check about the exemplar info on prometheus ui, you will find exemplar info can not be displayed

Expected Result

Actual Result

Collector version

0.75.0

Environment information

Environment

OS: (e.g., "Ubuntu 20.04")
Compiler(if manually compiled): (e.g., "go 14.2")

OpenTelemetry Collector configuration

No response

Log output

No response

Additional context

No response

[github-actions]

Pinging code owners:

• connector/spanmetrics: @albertteoh @kovrus

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