Rename "IStorage" methods for v4

Hello,

I noticed that the cloud-storage interface has the following methods:

    createBucket(bucketName: string): Promise<void>;
    bucketExists(bucketName: string): Promise<boolean>;
    deleteBucket(bucketName: string): Promise<void>;

These method names suggest that new buckets are getting created, checked for existence, or deleted within a single data-partition. However, the GC and Baremetal implementations are different -- a data-partition is expected to work with its own pre-created bucket instead of creating new ones. This discrepancy between the method names and their actual functionality could lead to confusion and misunderstanding.

A similar situation exists in the AWS implementation, where comments had to be added to clarify that 'bucketNames' are actually BLOBs, which can be seen here.

I propose that we consider renaming these methods to more accurately reflect their functionality and create a better alignment with the actual implementation.

Thank you.