Credentials extraction from specified path or from AWS CLI

[DenisaCG]

Added credentials extraction directly from where they are stored for AWS CLI users, namely in ~/.aws/credentials, as well as from a user specified path to a file which contains their credentials.

Now, the extension supports:

• setting credentials in jupyter_notebook_config.py
• direct extraction of credentials for the AWS CLI tool users
• extracting credentials from a user specific file.

While the AWS CLI tool credentials extraction only benefits S3 users, the other two options keep the architecture open for other kind of drives as well.

This PR also adds onto the existing content manager structure, in order to also allow for short-term credentials, namely making use of the session_token.

[github-actions[bot]]

:point_left: Launch a Binder on branch DenisaCG/jupyter-drives/credentialsCLI

[DenisaCG]

Thanks for your review @trungleduc!

As we need this functionality for the current version, I will merge this PR and later open a new one where I will make the suggested improvements.