Include all extensions in all flavours (with some disabled by default but available to be toggled by admin or users)

[mayel]

• include extensions from all flavours when compiling
• auto-disable extensions from other flavours
• include them in settings so they can be toggled on
• run things that usually are done on app startup (eg. gathering behaviour modules, so things like the nav are updated, though that may be better to include on startup, and just hide the disabled ones since we need to do that for user-disabled ones anyway)
• add more flexibility to instance-level toggles (by admin):
  • enable for all
  • available but disabled by default
  • force-disable for all users

[mayel]

A message is now shown on startup indicating something like this:

NOTE: these extensions are not part of the classic flavour and will be available but disabled by default: 
[:bonfire_api_graphql, :bonfire_ui_topics, :bonfire_ui_groups,
 :bonfire_valueflows_api_schema, :bonfire_valueflows,
 :bonfire_valueflows_observe, :bonfire_ui_valueflows, :bonfire_ui_coordination,
 :bonfire_ui_kanban, :bonfire_upcycle, :bonfire_breadpub, :bonfire_geolocate,
 :bonfire_quantify, :bonfire_pages, :absinthe_client, :towel, :absinthe,
 :bonfire_ui_reflow]