New features, refactoring and replacement of Flask by Quart

[benoit-garcia]

This PR contains several changes:

New features:

• Two new routes were added to support Terraform operations. Terraform need to be installed on the running host. Beware that terraform operations may take some time. I advise increasing the time out duration on gitea if you plan to use it. This is done by editing the value of the DELIVER_TIMEOUT parameter in the webhook section.
• Allow the use of SSH instead of HTTP(s) when cloning repositories. The default setting remains HTTP(s).

Refactoring

• In order to improve readability of code, and to ease the addition of new routes, the application is now split in several files.
• Inclusion of __pycache__ and .venv directories to the list of files ignored by git.
• Creation of a .editorconfig file to helps maintaining consistent coding styles (see editconfig.org for more information).
• The main application is now defined as a module (see the runner directory, however the starting script (tea-runner.py) can be use all the same.

Breaking changes:

In order to use background tasks in the future, tea-runner is now using:

• Quart instead of Flask.
• Hypercorn instead of Waitress.

Code style

• Imports were re-ordered, following PEP-0008.
• All code has been formatted using Black.