Add entrypoint to pyproject

pyproject.toml

@@ -12,6 +12,9 @@ dependencies = [
     "musicbrainzngs (>=0.7.1,<0.8.0)"
 ]
 
+[project.entry-points."mopidy.ext"]
+smartplaylists = "mopidy_smartplaylists:Extension"
+
 [tool.poetry]
 
 [tool.poetry.group.dev.dependencies]