[doc] Update index documentation to not only realtime data lake

[JingsongLi]

Apache Paimon is a lake format for building Lakehouse Architecture for both streaming and batch
operations. Paimon provides large-scale data lake storage for analytics, realtime streaming updates
powered by LSM (Log-structured merge-tree) structure, and multimodal data management for AI workloads
— all in a single unified format.

Large-Scale Data Lake

Paimon is built for huge analytic datasets. A single table can contain tens of petabytes of data, and even
these huge tables can be read efficiently without a distributed SQL engine.

• Time travel enables reproducible queries that use exactly the same table snapshot, or lets users easily
  examine changes. Version rollback allows users to quickly correct problems by resetting tables to a good state.
• Scan planning is fast — data files are pruned with partition and column-level stats, using table metadata.
  File Index (BloomFilter, Bitmap, Range Bitmap) and aggregate push-down further accelerate queries.
• Schema evolution supports add, drop, update, or rename columns, and has no side-effects.
• Rich ecosystem — adds tables to compute engines including Flink, Spark, Hive, Trino, Presto, StarRocks, and
  Doris, working just like a SQL table.
• Incremental Clustering with z-order/hilbert/order sorting to optimize data layout at low cost.

Realtime Data Lake

Paimon's Primary Key Table brings realtime streaming updates into the lake architecture, powered by the LSM
(Log-structured merge-tree) structure.

• Large-scale streaming updates with very high performance, typically through Flink Streaming.
• Multiple Merge Engines: Deduplicate to keep last row, Partial Update to progressively complete records,
  Aggregation to aggregate values, or First Row to keep the earliest record — update records however you like.
• Multiple Table Modes: Merge On Read (MOR), Copy On Write (COW), and Merge On Write (MOW) with Deletion Vectors
  for flexible read/write trade-offs.
• Changelog Producers (None, Input, Lookup, Full Compaction) produce correct and complete changelog for merge
  engines, simplifying your streaming analytics.
• CDC Ingestion from MySQL, Kafka, MongoDB, Pulsar, PostgreSQL, and Flink CDC with schema evolution support.

Multimodal Data Lake

Paimon is a multimodal lakehouse for AI. Keep multimodal data, metadata, and embeddings in the same table and query
them via vector search, full-text search, or SQL.

• Data Evolution for efficient row-level updates and partial column changes without rewriting entire files — add
  new features (columns) as your application evolves, without copying existing data.
• Blob Table for storing multimodal data (images, videos, audio, documents, model weights) with separated storage
  layout — blob data is stored in dedicated .blob files while metadata stays in standard columnar files.
• Global Index with BTree Index for high-performance scalar lookups and Vector Index (DiskANN) for approximate
  nearest neighbor search.
• PyPaimon native Python SDK with no JDK dependency, seamlessly integrating with the Python AI ecosystem
  including Ray, PyTorch, Pandas and PyArrow for data loading, training, and inference workflows.

[XiaoHongbo-Hope]

+1