Author winget manifest YAML for fallout-agent

Parent: #121

Author the three winget manifest YAML files for `Fallout.Agent` (`Fallout.Agent.installer.yaml`, `Fallout.Agent.locale.en-US.yaml`, `Fallout.Agent.yaml`) to the [microsoft/winget-pkgs](https://github.com/microsoft/winget-pkgs/tree/master/manifests/) schema.

## Definition of done

- Manifests stored in `eng/winget/` (path TBD during implementation) inside this repo.
- `winget validate --manifest eng/winget/` passes locally.
- Manifests rendered as templates with placeholders for version and installer URL so the release pipeline (__W4__) can substitute on tag.
- Schema version pinned to the current winget-pkgs `manifestVersion`.