Enhancement - Support integration with Azure Kubernetes Fleet Manager

**Is your feature request related to a problem? Please describe.**
We from the Azure Kubernetes Fleet Manager would like to make `draft` support automated deployment like how it currently works with an AKS cluster. Anybody who wishes to setup an automated deployment onto a fleet resource with a hub resource can then propagate their deployment to its fleet member cluster.

Note that resource propagation is not in the scope of this work.

**Mention what platform you want to support the new feature**
az-extension, oss draft, and potentially vscode

**Describe the solution you'd like**
`draft setup-gh`
`draft create`
`draft generate-workflow`
`draft validate`
would work with a fleet resource in addition to an AKS cluster. This means `draft` needs to assign a Fleet RBAC role for the app in addition or instead of the current contributor role.

We also aim at bringing this enhancement to `azure-cli` so that we can use draft consistently with aks (i.e. we can use `az fleet draft` to set up an automated deployment on a Fleet resource).

**Additional context**
There are a couple of things that need to be aligned before a PR that enables this feature can be submitted:
1. Whether we still want to make `draft` works with all the resources in the resource group (`setup-gh` currently assigns _contributor_ with the whole resource group as the scope) or whether we want to shift to work with an individual resource now (i.e. a single AKS cluster or a single Fleet resource).
- If we move to an individual resource approach, how do we support specifying a resource name, ID or type? This will allow `draft` to generate different templates depending on the resource type.
- If we're not doing that, can we simply assign both `Azure Kubernetes Fleet Manager RBAC Writer` and `Contributor`? You might already have a plan to move to a smaller RBAC role like `AKS RBAC writer`.
2. For any additional templates we need to add for Fleet, do you prefer having them in the same folders as the current templates now or do you prefer having them separated?