feat: migrate setup.py to pyproject (with hatch backend), update package metadata and update publish workflow

[kbdharun]

Changes

Workflow side

• Restrict publish workflow's PyPI publish job to execute in this repo only and not in forks.
• Migrate from legacy pep517.build to build and update arguments for it (see below build log for more info).

Setup and pyproject

• Replace legacy setup.py setup for a more versatile pyproject.toml setup.
• Update build backend from setuptools to hatch as it compliant with the latest PEP versions (see linked core metadata file) and is very feature rich, fast and versatile.
  • I migrated the old setup.py contents to pyproject.toml using hatch new --init command.
  • Then I added keywords field and updated the classifiers.

Miscellaneous

• Misc: add workflow status badges to README.
• Bump client specification to 2.3, I left version as it is since it's bumped in Managor's PR.