Add the changelog entry for #1521

changelog.d/1521-provider-labels.md

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+- Name the provider that answered in the Cockpit Contact counts and the
+  Contacts list, as the Layers panel does, marked `FALLBACK` or `STALE` when
+  it is. The counts no longer read OpenSky while flights come from the adsb.lol
+  fallback, and vessels no longer always read AISStream (German, @gekh, #1521).