[SVS] Add Tiered SVS index implementation

[rfsaliev]

Implemented Tiered version of Scalable Vector Search index (TieredSVSIndex)

• Vectors moved to backend in 1 background job as a bulk
• Add basic unit tests for SVS tiered index
• Add Python binding for SVS Tiered index
• Backend index synchronized for deleted vectors

Main objects this PR modified

1. New class TieredSVSIndex
2. Tiered factory modified to support TieredSVSIndex

• [x] This PR introduces API changes
• [ ] This PR introduces serialization changes

TODO:

• [ ] Uncomment and fix unit tests copy-pasted from HNSW-tiered or remove if not relevant.