Unify logic for credentials (GONRG-539)

Description:

• Credential classes were moved into gcp-core-lib.
• Changed a version 'gcp-core-lib'.
• Changed unit tests.

How to test:

Check business logic.

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

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.

Other comments:

Any comments to approvers here