[ECS][Request]add support for LogConfig Options "Type" and "Config:Labels"

### Summary

I would like the ability to add one (or both) of "Type" and "Config:Labels" to the logs produced by the ECS Agent. The purpose of this is to have greater control over the log destination and log format. As an example, one of the companies I work with uses the logConfig as follows for all containers:

```
"LogConfig": {
"Type": "json-file",
"Config": {
"labels": "container_name,git_sha"
}
},
```

The purpose of the labels is that Docker logdriver will create logs that have the value `container_name` embedded in JSON output and this can be then used to filter logs based on particular values (for instance, all of their containers are assigned a container name).

### Description
See above.

### Expected Behavior
I was hopeful that I would be able to assign "labels" to the log files written by the ECS Container Agent when launched on Amazon Linux 2 / by the amazon-ecs-init RPM.

### Observed Behavior
I was unable to assign "labels" to the logfiles written by the ECS Container Agent.

### Environment Details

Amazon Linx Version:
```
[root@ip-10-130-71-144 systemd]# uname -a
Linux ip-10-130-71-144.us-west-2.compute.internal 4.14.123-111.109.amzn2.x86_64 aws/amazon-ecs-init#1 SMP Mon Jun 10 19:37:57 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
```

Docker Version:
```
[root@ip-10-130-71-144 systemd]# docker --version
Docker version 18.06.1-ce, build e68fc7a215d7133c34aa18e3b72b4a21fd0c6136
```

ECS Agent:

```
"Image": "amazon/amazon-ecs-agent:latest"
"Image": "sha256:267bac512a39389e6ad2f0b9dfd04153c6950da89a88037ec32490eaeeee5f3a"
```

No repository files, tests, or implementation entry points are named. Start by locating the ECS Agent handling for container log configuration and compare its supported options with Docker's Type and Config:Labels behavior; done means those options can be assigned and produce the requested labeled log output.

Written by the indexing model from the issue text.