[Fargate] [Nitro-backed tasks]: describe request here

We already use Fargate. For security purposes we would like to use _Nitro-backed tasks_ on Fargate in GovCloud (US).

### Community Note

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**Tell us about your request**
What do you want us to build?
_Nitro-backed tasks_ on Fargate in GovCloud (US)

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
What outcome are you trying to achieve, ultimately, and why is it hard/impossible to do right now? What is the impact of not having this problem solved? The more details you can provide, the better we'll be able to understand and solve the problem.

**Are you currently working around this issue?**
How are you currently solving this problem?

**Additional context**
Anything else we should know?

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

Start with the request for Nitro-backed tasks on Fargate in GovCloud (US) and determine the current Fargate and GovCloud support boundaries. No files, tests, or implementation entry points are named, so the first step is to identify the relevant service roadmap or implementation owner. Done would mean a defined, maintainable path to providing Nitro-backed Fargate tasks in GovCloud.

Written by the indexing model from the issue text.