Allow anonymous posting based on group membership

[Moin]

This was implemented as part of

Changes coming to settings for giving access to features (from trust levels to groups)

Many features in Discourse rely on a setting to give access by trust level. This has proven to be too inflexible over the years, so we are moving to a new practice of giving access to members of specific groups instead. We will now begin moving existing settings relying on trust levels so they instead rely on groups - see the list below that we are targeting. Some settings will remain trust level based where it makes sense. As we move along we will update the list and add replies here. Do let u…