[ECS] Allow overriding docker labels for containers

### Summary

Support for overriding docker labels for per container task execution.

### Description

For cases where, containers are used for cron style workflows, the task definition will be shared. Being able to override override docker labels for task execution will allow us to set job level parameters.

### Expected Behavior

### Observed Behavior

### Environment Details

### Supporting Log Snippets

The issue describes a requested ECS capability but names no repository files, tests, or implementation entry points. Start by determining where task-execution container overrides are defined and how Docker labels are represented; done would mean agreeing on and implementing a supported per-container label override for shared task definitions.

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