options to disable setting profile info

[ara4n]

# If enabled, don't let users set their own display names/avatars
# other than for the very first time (unless they are a server admin).
# Useful when provisioning users based on the contents of a 3rd party
# directory and to avoid ambiguities.
#
# disable_set_displayname: True
# disable_set_avatar_url: True

[dbkr]

I would love if these could be disable_set_displayname with default: True rather than negative. Otherwise lgtm.

[localguru]

@hawkowl Why has this patch been deleted? That would be exactly the feature I need. When authenticating e.g. against an IDP, it makes sense to set the display name when creating the user and not to allow the user to change it later. See also #5241

[eMPee584]

Mhh why is this feature in the dinsic branch but not in master? (ref #5267)