Add JSON and NDJSON output formats

[zmoog]

Motivation

Using this axios CLI in combination with other tools requires having JSON-based output formats.

For example, I want to be able to do something like this:

$ axios grades list --output-format json | \
    jq '{"grades": .}' | \
    jinja -d - -f json templates/axios/grades.j2 | \
    tgm message send --chat-id ${CHAT_ID}

Change description

Move the formatting logic into a dedicated result module. In this module, the GradesListResult class will be responsible for formatting the result of the grades list command.

Additional Notes

• Related to Send latest grades from Axios automator#2

Reviewer checklist

• PR address a single concern.
• PR title and description are appropriately filled.
• Changes will be merged in main.
• Changes are covered by tests.
• Logging is meaningful in case of troubleshooting.
• Docs are updated (at least the README.md, if needed).
• History is clean, commit messages are meaningful (see CONTRIBUTING.md) and are well-formatted.