UPDATE January 2022: The official HEOS integration had grouping features implemented as of Home Asssitant version 2021.12 and this custom integration should not be necessary anymore. It may be deprecated after a time of testing. OBS! If using the mini-media-player card for grouping, note that platform must be changed from 'heos' to 'media_player' for the speaker_group setting.
This custom integration may be used for testing other features such as media browsing or similar, feel free to continue using it.