Add organization support to repos command

[OverkillGuy]

New --organization flag to signify all given "usernames" are private orgs. Adapts API URL to the organization path instead.

Not the best implementation, but a first draft to talk around

Fixes #75 (badly, no tests, overly vague, untested)

[OverkillGuy]

Tested PR just now in private org, fetched >2k repos infos flawlessly!

poetry run github-to-sqlite repos --organization github.db MYORG