Feat: basic configuration setup

[thekaveman]

What this PR does

• Adds a simple YAML-based config file, wrapper class, and commands to interact with the config
• Replaces the info command with config as the default
• Adds some basic usage docs in the README

Testing this PR

1. Checkout this branch
2. Rebuild and Reopen the devcontainer
3. Run tests from VS Code test runner
4. Call the CLI inside the devcontainer:

Initialize a config file

littlepay config

Switch to the prod environment

littlepay switch env prod

Print help info

littlepay -h

New version of #1

[github-actions]

Coverage report

The coverage rate went from 87.17% to 96.05% ⬆️
The branch rate is 94%.

98.42% of new lines are covered.

Diff Coverage details (click to unfold)

littlepay/commands/configure.py

91.66% of new lines are covered (93.33% of the complete file).
Missing lines: 29, 30

littlepay/commands/switch.py

100% of new lines are covered (94.11% of the complete file).

littlepay/main.py

100% of new lines are covered (91.66% of the complete file).

littlepay/config.py

100% of new lines are covered (100% of the complete file).

[machikoyasuda]

Runs on my machine:

• Commands

- Tests