fix(otel): Avoid concurrency issues when reporting metrics

[tomkerkhove]

Avoid concurrency issues when reporting metrics:

System.InvalidOperationException: Operations that change non-concurrent collections must have exclusive access. A concurrent update was performed on this collection and corrupted its state. The collection's state is no longer correct.
docker-scraper-1             |    at System.Collections.Generic.HashSet`1.AddIfNotPresent(T value, Int32& location)
docker-scraper-1             |    at System.Collections.Generic.HashSet`1.Add(T item)

• Switch to channels

Fixes #2169

[tomkerkhove]

Potential better alternative: https://learn.microsoft.com/en-us/dotnet/core/extensions/channels

[tomkerkhove]

/azp run Promitor CI - scraper agent

[azure-pipelines]

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