Enable Metrics for RabbitMQ Component

[eerhardt]

RabbitMQ's current version is 6.6.0, which doesn't have any meters/event counters.

However, they have an alpha 7.0 version out, which does have event counters - see https://github.com/rabbitmq/rabbitmq-dotnet-client/blob/a0321c6c2203cedeacdd5c1ec5bcdc924e85a842/projects/RabbitMQ.Client/client/logging/RabbitMqClientEventSource.Counters.cs#L51-L58.

When we have a RabbitMQ component that depends on v7, we should enable Metrics via these EventCounters.

[danmoseley]

For future ref their commit was rabbitmq/rabbitmq-dotnet-client@6e6ab3e and indeed it's only in v7+.

Looks like they're pretty early in their v7 so it will be a question of whether it's stable in time for us to ship with it.

[davidfowl]

@eerhardt backlog or will we get this in preview?

[eerhardt]

@eerhardt backlog or will we get this in preview?

I don't expect RabbitMQ v7 to be released before Aspire's 8.0 release. (But would be pleasantly surprised.)

[eerhardt]

We have support for RabbitMQ v7 now with #6770.

However, an issue is that we don't/can't use the OpenTelemetry.Instrumentation.EventCounters nuget package to pull EventCounters into OTel Metrics. See #2819 - OpenTelemetry.Instrumentation.EventCounters does not ship a "stable" version, which means our client integration library can't depend on the package (or else it can't be "stable").

Options we have to move forward here:

1. Push for RabbitMQ.Client to use System.Diagnostics.Metrics.Meter instead of (or in addition to) EventCounters.
2. "Vendor"/copy in the source code for OpenTelemetry.Instrumentation.EventCounters like we do for other opentelemetry-dotnet-contrib libraries.
3. Don't add the metrics for now and wait for OpenTelemetry.Instrumentation.EventCounters to go stable.

cc @samsp-msft @noahfalk