Add support for OpenTelemetry's service.namespace

[nosan]

As per the OpenTelemetry documentation (https://opentelemetry.io/docs/specs/semconv/attributes-registry/service), service.group does not exist. Instead, service.namespace should be used for this purpose.

service.namespace:

A string value having a meaning that helps to distinguish a group of services, for example the team name that owns a group of services. service.name is expected to be unique within the same namespace. If service.namespace is not specified in the Resource then service.name is expected to be unique for all services that have no explicit namespace defined (so the empty/unspecified namespace is simply one more valid namespace). Zero-length namespace string is assumed equal to unspecified namespace.

service.group is set up in both OpenTelemetryAutoConfiguration and OtlpMetricsPropertiesConfigAdapter

[mhalbritter]

service.group has been added in #39957. Currently it's only exposed via OTel and logging (without the field name).

To not break backwards compatibility, we should support both service.group and service.namespace for some time. service.namespace has been mentioned here, too.

[thecooldrop]

Hello @mhalbritter, may I be assigned this issue?

[mhalbritter]

Hello @thecooldrop, thanks for wanting to work on this. I think we should first merge #44394, otherwise there will be a lot of merge conflicts.

I'll assign you to the issue, but please hold off for now. Thanks!

[mhalbritter]

@thecooldrop I merged the PR, it's on main now.