added feature flag for container network metrics

[JVecsei1]

• Related to Apps network usage metrics missing cf-networking-release#64
• Feature flag to enable container network metrics implemented in this guardian PR.
• Addresses the comment in the diego-logging-client pointing out that this metric may not be of interest to everyone.
  • allow sending network traffic usage for app metrics diego-logging-client#82 (comment)

[geofffranks]

@JVecsei1 Would you be able to add a template test for this in spec/jobs/garden_spec.rb? You can run the tests via ./scripts/template-tests. The template tests look like they fail in ruby 3.2, but succeed in 3.1.1. You can also run run them inside the cloudfoundry/garden-runc-release CI docker image if you need an easier-to-grab ruby env.

[JVecsei1]

@JVecsei1 Would you be able to add a template test for this in spec/jobs/garden_spec.rb? You can run the tests via ./scripts/template-tests. The template tests look like they fail in ruby 3.2, but succeed in 3.1.1. You can also run run them inside the cloudfoundry/garden-runc-release CI docker image if you need an easier-to-grab ruby env.

@geofffranks yes, of course. I added a template test with f874df7.