Issue

We now have a feature that allow to add arbitrary key to the agent policy sent to the agent, elastic/kibana#159414 (comment)

I tried to set agent log level this way to Fleet managed agents, and it seems the agent is still logging at the default log level, when I run elastic-agent inspect I saw that my agent.logging.level: debug config is here, but it seems not used by the agent

Definition of done

• Logging level is taking into account the one in the policy
• Test confirming the logging level change is working as expected
• Test covering the logging level change from settings action too
• Test covering an unexisting logging level target