otel-collector example does not use metrics

[mx-psi]

Description

The example/otel-collector example mentions metrics on its README but it does not have any metrics export code since #1990.

Expected behavior

The example would either document how to use metrics or it would remove any mention of metrics from its description.

[Aneurysm9]

It looks like the metrics part of the example was removed when we were splitting up the OTLP exporter and never added back. We should probably create a separate example for metrics as we have included this example in the stable version set and cannot take a metrics dependency there until metrics are stable.

[fatsheep9146]

I'm new on OpenTelemetry, and when I search for demo examples, I found this issue. If this issue still need help, I've love to help with this. Is this ok for you? @Aneurysm9 @MrAlias

[Aneurysm9]

That would be great, @fatsheep9146. I'll assign this issue to you.

[fatsheep9146]

I've already tested the demo code for metrics otel-collector locally, but I'm not sure how to write this doc is the best.

1. Modify this existing 'otel-collector' example, complement with metric part
2. Add a new folder which name is 'otel-collector-for-metric' and put the code right there.

Which one do you suggest? @Aneurysm9

[fatsheep9146]

I have already make a seperate demo for otel-colletor and metric data. @mx-psi @Aneurysm9 @MrAlias