Add ability to seed multiple default users with configuration binding

[Kronos11]

This was a nice to have for our team as we wanted our whole team to have access to setup Toggles

[unaizorrilla]

Hi @Kronos11

As always! thanks for contribute this! I try to review asap!

[Kronos11]

@unaizorrilla updated based on your comments

[unaizorrilla]

Merged, thanks for contribute!

I do some minor changes like:

• Only one way to specify default subject
• Modify demo's docker-compose with new default users configuration section