Add displayName and description to PropertyMigration

[strangelookingnerd]

The UI of the administrative monitor for PropertyMigration seems to be broken since it is missing a display name:

This PR adds a display name and a descripton for the monitor:

I'd be happy to change the label / description to something more elaborate, suggestions are highly welcome.

Testing done

Manually verified the UI looks as expected.

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• Ensure that the pull request title represents the desired changelog entry
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[jglick]

Thanks, I had recently noticed this too. Weird that getDisplayName is not simply abstract.