[ECS][request]: Diagram icon for ECS Agent (+ Fargate Agent icon hopefully)

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**Tell us about your request**

We need icons for ECS Agent and Fargate Agent to tell about agents with nice diagrams.

**Which service(s) is this request for?**

ECS, Fargate

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**

There are no agent icons in the [AWS Architecture Icons](https://aws.amazon.com/architecture/icons/). So we always end up with an alternative shape with text and/or an emoji like :robot:

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

I use :robot: to put ECS Agent in my personal diagram, but need an official and fancy one.

**Additional context**

Kubernetes has a `kubelet` icon, for example.

Personally I love the mackerel-agent and the mackerel-container-agent's icons from [Mackerel](https://mackerel.io). They're really nice.

**Attachments**

Kubelet

mackerel-agent

mackerel-container-agent

Start by reviewing the AWS Architecture Icons collection linked in the issue and compare its ECS and Fargate coverage with the requested agent concepts. Done means the official icon set includes clear diagram icons for both ECS Agent and Fargate Agent; no repository files or tests are identified in the issue.

Written by the indexing model from the issue text.