Feature/275691446/update project requirements

[soulless-viewer]

Description

This PR was opened to clarify our project requirements.
Not all of them are accurate and justified, which can cause bugs or at least misunderstandings.

Changes

1. Minimum required Python version was downgraded from 3.9 (unjustified) to 3.7
   • Python versions <3.7 are not officially supported by dependent libraries. Their use can lead to unpredictable errors.
2. The Python version used in GitHub flow was also set as 3.7 to test on the oldest version
3. Minimum required google-api-python-client version was set as 2.68.0 *
   • Technically, the version should be at least 2.1.0, since it introduced resources on which we depend. However, it was decided to use the version that came out on a par with the beginning of our development
4. Minimum required google-auth version was set as 2.15.0 *
   • Also, it was decided to use the version that came out on a par with the beginning of our development

[halleysouza]

Thanks, please have a look on the README.md comment.

change will be addressed in a separated PR

[halleysouza]

lgtm