Lsm compare with 0.13.1

[zhangyue19921010]

Including the following modules:

1. Naming rules for Hudi Common LSM files and corresponding identification logic
2. Organization of FileGroup, FileSlice, Logfile and organization of fs view
3. Flink reading, writing, and Compaction
4. Spark reading, writing, and Compaction
5. Sort Merge Read and corresponding abstractions
6. LSM Rollback
7. LSM Clean
8. Various Record Mergers
9. etc..

[zhangyue19921010]

Hi @vinothchandar @danny0405 @xushiyan An initial PR has been submitted based on version 0.13.1, which should cover most of the core logic. However, the details may be incomplete and are for reference only. PTAL ：）

[hudi-bot]

CI report:

• 754ce62 UNKNOWN

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