Introduce GCS adapter for remote cache

What does this MR do?

Adds GCS support for caching mechanism

Why was this MR needed?

GCS doesn't work well with minio-go library, because of differences in S3 protocol implementations. This MR adds support for GCS using the GCS own API to create presigned URLs for uploading and downloading.

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated: http://review-docs-intro-xleo88.178.62.207.141.xip.io/runner/configuration/advanced-configuration.html#the-runners-cache-section
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

Closes #1773 (closed)