Support for PostgreSQL 14 to 18

What's changed

• Update google-cloud-bigquery (3.47.0), google-auth (2.62.2), google-auth-oauthlib (1.5.0)
• Require Python >= 3.10
• CI: test PostgreSQL 14 to 18 on Python 3.12 (#42 by @devrimgunduz)
• CI: update GitHub Actions and the Codecov uploader
• Build Multicorn from ShaheedHaque/multicorn2 pinned to the upstream v3.2 commit (pgsql-io/multicorn2 was removed)
• Publish the README as Markdown on PyPI

Install: pip install bigquery-fdw==2.2.0

Full changelog: 2.0...2.2.0