Description of the new feature/enhancement

Currently I believe it is not possible to add a manifest for an app from the msstore source (if this is wrong, please correct me and close this issue). To install one of these apps, the user must type something like winget install 9PHJSNP1CZ8J, which is not exactly intuitive. Devs who provide packages for the MS Store should be able to provide a moniker to make the install easier.

Proposed technical implementation details (optional)

Allow a dev to use msstore as the source for a manifest. This manifest would be extremely basic: it would simply map a store product ID to a moniker, possibly customize the description text, but it would not have version numbers. Instead it would be published at, e.g. /manifests/k/Kiwix/KiwixJS/9PHJSNP1CZ8J (i.e. /manifests/[alpha]/[publisher]/[product]/[msstore-product-id]).