• activemq 'classic' doc
• activemq 'artemis' : bonus, can be done as a follow-up: doc

Proposal

Use the activemq.* namespace for all metrics:

• do not use messaging.activemq.* namespace (Messaging: adopt system-specific naming practices similar to DB semantic-conventions#1892)

Reuse when possible messaging semconv definitions, for example messaging.destination.name, this implies a few expected changes in the future

• messaging.system = activemq, we expect it to be stabilized as messaging.system.name Messaging: adopt system-specific naming practices similar to DB semantic-conventions#1892
• activemq.destination.type might be used to indicate if it's a queue or topic, there is currently no semconv attribute to reflect this (Messaging: record queue vs topic behavior correctly semantic-conventions#1220), there was one in the past but it has been removed.