Enable multiple resources in single resource manifest

[SteveL-MSFT]

Summary of the new feature / enhancement

Been a common ask by partner teams.

Proposed technical implementation details (optional)

I think the simplest solution is to allow a manifest to contain an array of resource manifests

[michaeltlombardi]

Thinking about this, I would prefer that we have a (lightweight) wrapper object, like:

{
    "$schema": "https://aka.ms/dsc/schemas/v3/resource/manifest.json",
    "resources": [
        {
            "type": "Example/Foo"
            // elided fields
        },
        {
            "type": "Example/Bar"
            // elided fields
        },
        {
            "type": "Example/Baz"
            // elided fields
        }
    ]
}

Where we update the resource schema to use the oneOf keyword pointing to the correct schema. Primarily, my thinking is:

1. I don't think it makes sense to support different resources in the same manifest with different schema versions.
2. Getting the enhanced authoring schema to deal nicely with the array-of-resources model will be painful compared to the wrapper.
3. We could optionally consider (later, not required for initial implementation) supporting field definitions at the top level defining defaults for lower-level, which would reduce duplication (such as setting author, version, etc).

[SteveL-MSFT]

Current proposal, have a new .dsc.resourcelist.json (or yaml) that is an array of manifests. A resourcelist manifest will have a single property resources which is an array of nested manifest objects.