Workflow Roles implemented (GONRG-720)

Description:

As a part of GONRG-680:

• Changed user's storage roles to workflow roles. Issue (#41)
• Fixed unit tests.

As a part of GONRG-727:

• Added README for datastore-gcp implementation with tests

How to test:

Code has been tested by unit and integration (EPAM env) tests. Full guide for integration tests now available in README

Changes include:

• Refactor (a non-breaking change that improves code maintainability).
• Bugfix (a non-breaking change that solves an issue).
• New feature (a non-breaking change that adds functionality).
• Breaking change (a change that is not backward-compatible and/or changes current functionality).

Changes in:

• GCP
• Azure
• AWS
• IBM
• Core

Dev Checklist:

• Added Unit Tests, wherever applicable.
• Updated the Readme, if applicable.
• Existing Tests pass
• Verified functionality locally
• Self Reviewed my code for formatting and complex business logic.