Create ENTSOE Tariff module

[jorg-vr]

This PR creates the initial project, with a first basic module for tariffs that directly uses the entsoe-py module as datasource.

As this is the first module, this will also contain some other changes:

Repo setup

• Complete 'develop' chapter in README
• testing framework with coverage calculation and github action
• precommit typing an styling
• Demo project for manual testing
• Introduction of libraries
• Automatic docs and API schema generation

Code

• Cofy app for module registration
• Actual Tariff module

closes #2