Add a new E2E test to confirm that Elastic Agent component logs can be shipped to Fleet

[cmacknz]

What do we want to do and why?

• Depends on E2e proposal #2292

Implement an E2E test that enrolls an agent in Fleet and ensures that logs are shipped to the expected set of logs datastreams. This tests automates enrolling an agent in Fleet and manually inspect the logs messages in the UI box below.

1. Enrolls an Elastic Agent in Fleet. The system integration and agent log monitoring should both be enabled by default.
2. Confirms that log messages are populated for the logs-elastic_agent-default, logs-elastic_agent.filebeat-default and logs-elastic_agent.metricsbeat-default datastreams:

• Ensure that the log message "Parsed configuration and determined agent is managed by Fleet" can be queried from logs-elastic_agent-default.
• Ensure the log message metricbeat start running. can be queried from logs-elastic_agent.filebeat-default
• Ensure the log message filebeat start running. can be queried from logs-elastic_agent.metricsbeat-default.

4. Confirms that no error level logs or panics can be queried from any of the datastreams above.
5. Unenrolls the Elastic Agent.
6. Uninstalls the Elastic Agent.

The steps in this test touch a large surface area of the agent and Fleet product and would have automatically detected several recent regressions, notably:

• Deadlock on exit after receiving SIGTERM #2394
• Filebeat monitoring enters infinite error loop for "closed processor" beats#34716

Definition of done

• E2E test using our new framework is in place to validate the mentioned scenario.

[cmacknz]

This test should also change the agent log level to debug and confirm that each process generates at least one debug log. We'll have to look at some representative logs to find a few that are always generated.

[amitkanfer]

Marking this one as P0 as we're keep breaking our debug logs

[amitkanfer]

@pierrehilbert what's blocking us here?

[pierrehilbert]

Nothing anymore, just updated the status.

[fearful-symmetry]

Currently blocked by a handful of bugs and rough edges in the testing framwork. The biggest actual blocker is here: elastic/elastic-agent-libs#127