break publish-to-pypi into 2 jobs + add dependabot

[yunjunz]

Description of proposed changes

• build-n-publish-to-pypi.yml:

  • rename "publish-to-test-pypi.yml" to "build-n-publish-to-pypi.yml"
  • trigger for pull requests
  • split jobs into 2: "build-sdist-n-wheel" and "upload-to-pypi"
  • use upload/download artifacts to connect them, as used in pysolid

• add .github/dependabot.yml for auto update

Reminders

• Pass Codacy code review (green)
• Pass Pre-commit check (green)
• Pass Circle CI test (green)
• Make sure that your code follows our style. Use the other functions/files as a basis.
• If modifying functionality, describe changes to function behavior and arguments in a comment below the function declaration.
• If adding new functionality, add a detailed description to the documentation and/or an example.