* fix: change public role like gamma procedure

* lint and updating UPDATING with breaking change

* fix updating text

* add test and support PUBLIC_ROLE_LIKE_GAMMA

* fix, cleanup tests

* fix, new test

* fix, public default

* Update superset/config.py

Co-authored-by: Ville Brofeldt <33317356+villebro@users.noreply.github.com>

* add simple public welcome page

Co-authored-by: Ville Brofeldt <33317356+villebro@users.noreply.github.com>