Update backup_restore.md instructions for Google Cloud Storage bucket...

What does this MR do?

Add an instruction in the configuration for Google Cloud Storage backups which specifies the correct ACL parameter to use in creation of a bucket. The ACL default model option "Set object-level and bucket-level permissions" must be used or backups will fail to upload.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer