[Elastic Agent] Remove dynamic: false from index templates

[kpollich]

Previously, we set dynamic: false in the mappings for the Elastic Agent integration's data streams, e.g.

integrations/packages/elastic_agent/data_stream/filebeat_logs/manifest.yml

Lines 1 to 7 in 98a8e95

	title: Elastic Agent
	dataset: elastic_agent.filebeat
	type: logs
	elasticsearch:
	index_template:
	mappings:
	dynamic: false

This was, at the time, a decision made to prevent an explosion of fields early in Agent/Fleet's product lifecycle. Today, we have mechanisms like dynamic field limits, and can rely on ECS templates for much of the field mappings for logging data streams.

We should explore removing dynamic: false from the Elastic Agent integration's data stream mappings as an act of technical debt cleanup.