Refactor Beat instantiation and setup

[leehinman]

createBeater and configure do most of the work setting up a Beat.

These functions do things that prevent using these functions to instatiate multiple beats within the same process.

• metrics registry
• management registry
• telemetry registry
• setting go runtime variables
• diagnostic hooks

This needs to be refactored so multiple Beats can be started in the same process without conflicts or overwriting registries.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)