Can't easily Map collection from .NET Standard to MetadataControl?

## Describe the bug

Since we've been doing a lot more with the MVVM Toolkit lately, I was thinking about the scenario where your data model may be coming from .NET Standard. E.g. having a list of items for tags or something.

Currently, you'd have to hard create a new list of `MetadataItem` from that list and make sure you observe any changes to re-map yourself.

It'd be nice if we could take in any collection of items and map to the properties we need instead. Like `ComboBox` does with `DisplayMemberPath` for instance. Though this may be a bit odd for commands?

It's also a lot more reflection heavy to do it that way... And I don't think we'd want a general `MetadataItem` type class in our .NET Standard libraries to be tied specifically to a control in our UI library...

Do we see this as an issue with using the control?

## Environment

NuGet Package(s): 7.1.0-rc1

Package Version(s):

Windows 10 Build Number:

- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] May 2020 Update (19041)
- [ ] Insider Build ({build_number})

App min and target version:

- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] May 2020 Update (19041)
- [ ] Insider Build ({build_number})

Device form factor:

- [ ] Desktop
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio version:

- [ ] 2017 (15.{minor_version})
- [ ] 2019 (16.{minor_version})
- [ ] 2022 (17.{minor_version})

## Additional context

FYI @vgromfeld @Sergio0694