Gcp Stabilize File Service (GONRG-1522)

Description:

Stabilization after MR Integrate Delivery Service API into File Service:

• Fix DownsopedCredentials for cloud run(use application default credentials instead of service account credentials).
• Fix DeliveryStorageServiceImpl (unhardcode target bucket for connection string)
  Stabilization after MR GCP Integration test changes :
  
• Remove specific provider dependencies from file-test-gcp
• Update README.md (added new env variables for int tests)

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.