[ECS] [feature request]: Support container restart policy for bridge mode FireLens log router containers

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**Tell us about your request**

Currently, when using the ECS FireLens feature there are two env vars set on the application container so that it can directly log to the fluent-bit log router container (ie, the container with the firelensConfiguration object) without using stdout: FLUENT_HOST and FLUENT_PORT. (see ECS doc for more details: https://docs.aws.amazon.com/AmazonECS/latest/developerguide/firelens-docker-buffer-limit.html)

On the EC2 launch type in bridge network mode, the FLUENT_HOST env var is set to a dynamic IP address. This means that if the log router container has a restart policy, and it restarts, then it can get a new IP address, and the application container's FLUENT_HOST ip address will not be accurate anymore.

This means that writes from the application container to FLUENT_HOST can begin to fail after a restart of the FireLens log_router container.

**Which service(s) is this request for?**
ECS/EC2

**Are you currently working around this issue?**

Don't write directly to FLUENT_HOST when using CRP on the log router container in bridge mode.

**Additional context**

This could be fixed by using user-defined networks: https://github.com/aws/containers-roadmap/issues/184, because agent could then set FLUENT_HOST to be a DNS name rather than an ip address.