Add a reproducible workflow strategy compatible with soft-fork

[tgilon]

Closes open-energy-transition/cookiecutter-project#2.

Changes proposed in this Pull Request

To make the soft-fork strategy compatible with the concepts of the cookiecutter, it is suggested that the necessary files be included in the main repository. With this structure it should be easy to kick out projects as soft-forks.

Checklist

• I tested my contribution locally and it works as intended.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in config/config.default.yaml.
• Changes in configuration options are documented in doc/configtables/*.csv.
• Sources of newly added data are documented in doc/data_sources.rst.
• A release note doc/release_notes.rst is added.

[tgilon]

@siddharth-krishna @daniel-rdt @yerbol-akhmetov As discussed last week, here is the PR. Your feedback is welcome !

[siddharth-krishna]

Thanks, Thomas! This is a nice idea. I've left some minor comments. I'm also wondering if the first paragraph should say something about the soft fork strategy and link to the handbook?

[tgilon]

Thanks, Thomas! This is a nice idea. I've left some minor comments. I'm also wondering if the first paragraph should say something about the soft fork strategy and link to the handbook?

@siddharth-krishna I've added a new paragraph in the README.

[tgilon]

@pz-max I've updated the default licence to MIT. @martacki Do you have any other suggestions ?