Elastic Agent docker user should be numeric #11571
Description
Make the same change that was done for Beats in elastic/beats#41197 for Elastic Agent, for example the user below should be numeric instead.
This makes the container with more restricted security contexts using runAsNonRoot set to true which requires a numeric user to verify the user is not the root user.
Acceptance Criteria
Add a test that proves the agent containers can run as unprivileged in security contexts that set runAsNonRoot to true