Add default admin for first time deployments

[ayr-ton]

As a non-Okta User
When I connect to Kamu for the first time
I want to have a default admin user and password
So I can configure the first users that will use Kamu

Acceptance Criteria

Given I have no Okta environment variables
When I try to login with admin username and (sudo su) password
Then I should be able to access the system and the admin page with full capabilities

Is your feature request related to a problem? Please describe.

For non-Okta based deployments, we need to manually connect to the instance and run python manage.py createsuperuser for creating the first superuser.

The responsibility for deleting or changing the admin credentials should be at the first administrator.

Don't forgot to remove the mention for this issue from README.md