I was not sure what category to place this under so here is my background, I work for British Telecom and we have been using Foreman(1.24) with Puppet 5.5/6 infrastructure for about 65k agents, we use config groups and were planning to use environments going forward. But I believe both of these are not in Foreman 3.x by default but were going to be provided as plugins, is this correct?. If so, where can I find them please?
Yes, Puppet functionality was moved to a Plugin which is still installed in 3.0 by default and in later versions can be installed if needed. On updates it will be installed and kept.
So if updating no manual task should be required to keep Puppet functionality, as the data migration is done via hook in the installer.
If you are doing a new installation
--enable-puppet should be enough.