Python 2.7 support removed from setup-python in Github Actions

[saimedhi]

What is the bug?

Python 2.7 support removed from setup-python in Github Actions due to Python 2.7 being unsupported since January 1, 2020. Related issue: actions/setup-python#672

What is the expected behavior?

Two potential solutions to address the issue are:

1. Complete removal of Python 2.7 support in opensearch-py.
2. Implement a workaround by running the job inside a container to continue using Github hosted runners with Python 2.7.

[saimedhi]

Kindly provide your input and support by indicating your preferred option among the two choices mentioned above. Thank you :)

[wbeckler]

I propose we remove 2.7 tests asap to unblock GHA.
Then I think we should add back in 2.7 tests via a container, so that we don't accidentally break all Python 2 support in a minor release.

[dblock]

Yes, @saimedhi are you doing it?

[dblock]

Closing this in favor of #430 which is a more comprehensive issue on removing EOLed support.