✨ source-github: migrate to poetry

[alafanechere]

What

Relates to #34958

We want to make our connectors use poetry for dependency management (see tech spec)

This PR is migrating source-github to poetry.

How

• Create pyproject.toml and poetry.lock
• Pin main dependencies to the version used in the previous connector version
• Delete setup.py
• Update connector README.md with new instructions

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Name	Status	Preview	Comments	Updated (UTC)
airbyte-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 9, 2024 6:18pm

[github-actions]

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• PR name follows PR naming conventions
• Breaking changes are considered. If a Breaking Change is being introduced, ensure an Airbyte engineer has created a Breaking Change Plan.
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[alafanechere]

/approve-and-merge reason="poetry migration. green required CI check on 114f7a7"

[octavia-approvington]

After a careful ML study,
we think this looks okay.