Rename / Rethink project creation flags for WinAppSDK

[agniuks]

In the CLI, we currently distinguish between a UWP/WinUI2 app and WASDK/WinUI3 using the --winui3 flag. As support for more WinAppSDK configurations lands, we'll need a way to specify the kind of app that should be built in the CLI (unpackaged, MSIX packaged, WAP packaged). Proposed approach:

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we should likely rename / rethink this flag [--usewinui3]. I think we'll want something like:
--projectTemplate which takes a value of one of: uwp, winappsk-single, winappsdk-wap, etc.

Originally posted by @asklar in #9177 (comment)

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[chrisglein]

@AgneLukoseviciute does this fit in one of the phases for WinAppSDK? If so can you link it to the correct issue? Is it #9394?

[chrisglein]

Tricky aspect: This needs to work for all versions of RNW. So what we change it to needs to balance pre and post WinAppSDK.