Direct insert HFiles and Persist in-memory HFile tracking

We propose a new feature (a new store engine) to remove the .tmp directory used in the commit stage for common HFile operations such as flush and compaction to improve the write throughput and latency on object stores. Specifically for S3 filesystems, this will also mitigate read-after-write inconsistencies caused by immediate HFiles validation after moving the HFile(s) to data directory.

Please see attached for this proposal and the initial result captured with 25m (25m operations) and 1B (100m operations) YCSB workload A LOAD and RUN, and workload C RUN result.

The goal of this JIRA is to discuss with the community if the proposed improvement on the object stores use case makes senses and if we miss anything should be included.

Improvement Highlights
1. Lower write latency, especially the p99+
2. Higher write throughput on flush and compaction
3. Lower MTTR on region (re)open or assignment
4. Remove consistent check dependencies (e.g. DynamoDB) supported by file system implementation