Document enable_ecs_exec in the EcsUserCodeLauncher (#27457)

Summary:
Explain the config to set to enable shelling into tasks launched by the
ECS agent.

## Summary & Motivation

## How I Tested These Changes

## Changelog

> Insert changelog entry or delete this section.

docs/docs-beta/docs/dagster-plus/deployment/deployment-types/hybrid/amazon-ecs/configuration-reference.md

@@ -239,6 +239,8 @@ agent_queues:
 | config.server_ecs_tags | Additional ECS tags to include in the service for each code location. If set, must be a list of dictionaries, each with a `key` key and optional `value` key. |
 | config.run_ecs_tags | AAdditional ECS tags to include in the task for each run. If set, must be a list of dictionaries, each with a `key` key and optional `value` key. |
 | config.repository_credentials | Optional arn of the secret to authenticate into your private container registry. This does not apply if you are leveraging ECR for your images, see the [AWS private auth guide.](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/private-auth.html) |
+| config.enable_ecs_exec | Boolean that determines whether tasks created by the agent should be configured with the needed linuxParameters and permissions to use [ECS Exec](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-exec.html) to shell into the task. Also grants the `SYS_PTRACE` linux capability to enable running tools like py-spy to debug slow or hanging tasks. Defaults to false. **Note**: For ECS Exec to work, the task IAM role must be granted [certain permissions](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-iam-roles.html#ecs-exec-required-iam-permissions). |
+
 
 ### isolated_agents properties