fix(user model): Fix default password generation.

[crankynetman]

Django is deprecating the make_random_password() method so we need to roll our own eventually, might as well now. Also we need to change the allowed characters for the DB secret as it keeps killing the django env library.

[github-actions]

File	Coverage
All files	83%	✅
config/consumers.py	78%	✅
config/urls.py	69%	✅
config/settings/base.py	69%	✅
config/settings/local.py	73%	✅
scram/route_manager/admin.py	85%	✅
scram/route_manager/models.py	70%	✅
scram/route_manager/views.py	88%	✅
scram/route_manager/api/serializers.py	73%	✅
scram/route_manager/api/views.py	83%	✅
scram/shared/shared_code.py	56%	✅
scram/templates/403.html	91%	✅
scram/templates/404.html	91%	✅
scram/templates/base.html	99%	✅

Minimum allowed coverage is 50%

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