Pass Coogle Cloud credentials via options (GONRG-397)

Adds ability to pass Coogle Cloud credentials via OpenVDS options

Type of change

• Bug Fix
• Feature

Does this introduce a change in the core logic?

• [NO]

Does this introduce a change in the cloud provider implementation, if so which cloud?

• AWS
• Azure
• GCP
• IBM

Does this introduce a breaking change?

• [NO]

What is the current behavior?

Credentials can be provided only via ADC (GOOGLE_APPLICATION_CREDENTIALS environment variable)

What is the new/expected behavior?

Credentials can be passed to GoogleOpenOptions structure

Have you added/updated Unit Tests and Integration Tests?

• [NO]

Changes:

• GoogleOpenOptions structure has been extended to handle credentials;
• IOManagerGoogle has been extended respectively.