TiDB provider supports expanding PD and TiKV storage

The TiDB provider now supports expanding storage for the Placement Driver and TiKV components, and rejects any attempt to shrink those volumes to prevent accidental data loss.

Previously, storage changes were passed through unvalidated, which could either silently fail or trigger unsupported shrinking operations. The provider now validates storage size changes during sync: expansion is allowed (handled by the TiDB Operator v2), while shrinking is rejected immediately with a clear error.

Storage expansion support is available now in TiDB provider v0.1.2.