[Elastic Agent] Accept logs path configuration

[simitt]

The Elastic Agent ignores the passed in --path.logs=xyz. This can be problematic for read-only environments, for example when running in a read-only docker container where all write actions are expected to go to bind mount only.

Not only the Elastic Agent logs but also the logs of the running sub processes need to be configurable.

This is related to #24160 and also required for 7.13.

Reproduce

• change docker entrypoint to exec {{ .BeatName }} container --path.logs ${LOGS_PATH} --path.config ${CONFIG_PATH} $@"
• run cloud command

docker run -it \
  --env LOGS_PATH=/app/logs/ \
  -v <your-path>/app:/app <image-ID>

and check that logs are not written to configured location

• run cloud command

docker run -it \
  --env LOGS_PATH=/app/logs/ \
  --env CONFIG_PATH=/app/config \
  -v <your-path>/app:/app <image-ID>

and check that agent logs are written to configured location, but sub process logs are missing.

This is required for the elastic cloud setup.

I have only checked this with docker.

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[simitt]

update: when passing in --path.logs and --path.config the elastic-agent logs are written to the logs path; this should not be connected to whether or not a config path is passed in.

The logs from the subprocesses are neither in the default log directory nor in the location set with the --path.logs.

updated the description accordingly