[Discuss] Automatically populate base fields

Related: https://github.com/elastic/integrations/pull/2939#discussion_r839278631

All packages must define base fields (`data_stream.type`, `data_stream.dataset`, `data_stream.namespace`, `event.module`, `event.dataset`, `@timestamp`). Values of these fields are constant for every integration and it doesn't make much sense to keep that information in the package.

The goal of this issue is to discuss the possibility of populating them with Fleet.

Bonus points:

Where should we store [agent.yml](https://github.com/elastic/integrations/blob/main/packages/activemq/data_stream/audit/fields/agent.yml), which also seem to be duplicated across many (all?) packages.

cc @ruflin @joshdover @lalit-satapathy (as you stumped over that issue recently)