[Fargate] [request]: Need capacity guarantee for Fargate

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**Tell us about your request**
Provide a way to guarantee capacity for Fargate clusters.

**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?**
In case of a disaster in my primary AWS region, I want to be able to make sure I have reserved capacity for my Fargate clusters in my DR region.

**Are you currently working around this issue?**
How are you currently solving this problem? No workarounds

Start by reviewing the request for guaranteed Fargate capacity and its disaster-recovery use case in a secondary AWS region. Define what reserved capacity for Fargate clusters would mean and how success would be verified; the issue names no repository files, tests, or implementation entry point.

Written by the indexing model from the issue text.