Copilot-cli: Feature request: allow sidecars to be marked as non-essential

[bvtujo]

As described in #2065, we should allow customers to mark sidecars as non-essential so that their exiting doesn't cause the task to become unhealthy.

To do this, we should add an optional field to our sidecars map:

sidecars:
  nonessentialSidecar:
    image: ecr.aws/image
    essential: false

This will cause the Essential property of the container definition to be rendered in the task definition.

[efekarakus]

This is now released in https://github.com/aws/copilot-cli/releases/tag/v1.5.0! 🚀 Thank you @git823 !