Renamed repo & team

[kaikreuzer]

Just FTR: As we now have version 3 on master, I have renamed this team to @openhab/add-ons-maintainers and also the repo from openhab2-addons to openhab-addons. No worries, Github still supports the old name, so this should not cause any links to break. For new links to be created, please directly use the new repo name openhab-addons, though.