Consider integration with Flux via a "Ytt Controller"

**Describe the problem/challenge you have**
I really like working with ytt and I usually use it together with kapp-controller. Still, I'm afraid many organisations might miss out on the great power of ytt because of the challenge to integrate it in their already-established GitOps workflow based on Flux. And that would limit a wider adoption of ytt.

**Describe the solution you'd like**
Flux is based on highly modular toolkit. In particular, the Source Controller provides support for different types of artefacts (Git, OCI, buckets), the Kustomize Controller provides support for Kustomize-based deployments, and Helm Controller for helm releases. Perhaps it could be an idea to introduce a **Ytt Controller** component in the GitOps Toolkit used by Flux. What do you think?

**Anything else you would like to add:**
In a recent community meeting, there was a conversation around integration possibilities with Flux and some of the resulting ideas are gathered in https://github.com/carvel-dev/kapp-controller/issues/1048.

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Start by reviewing the Flux Source Controller, Kustomize Controller, and Helm Controller references in the issue, then read the linked kapp-controller issue 1048. The issue does not identify files, tests, or a settled scope; completion would require an agreed design and prioritized plan for Flux integration.

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