Refactor the project structure to follow the same from other Safe projects

[Uxio0]

Is your feature request related to a problem? Please describe.
Structure of the project does not follow any standard.

Provide references to the feature you are implementing that requires this change
Project should follow the other Safe backend projects structure (like tx-service)

Describe the solution you'd like

• Use https://github.com/cookiecutter/cookiecutter-django#usage structure

Most relevant changes:

• Rename src folder
• Create folder for configuration
• Move conftest.py and manage.py to root folder
• Use full naming for Django apps (prepending the project name)

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.