Mention kRoundRobin in HISTORY.md (#10421)

Summary:
Update HISTORY.md for CompactionPri::kRoundRobin. Detailed implementation can be found in [PR10107](https://github.com/facebook/rocksdb/pull/10107), [PR10227](https://github.com/facebook/rocksdb/pull/10227), [PR10250](https://github.com/facebook/rocksdb/pull/10250), [PR10278](https://github.com/facebook/rocksdb/pull/10278), [PR10316](https://github.com/facebook/rocksdb/pull/10316), and [PR10341](https://github.com/facebook/rocksdb/pull/10341)

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10421

Reviewed By: ajkr

Differential Revision: D38194070

Pulled By: littlepig2013

fbshipit-source-id: 4ce153dc0bf22cd865d09c5429955023dbc90f37

HISTORY.md

@@ -5,6 +5,7 @@
 * Support using secondary cache with the blob cache. When creating a blob cache, the user can set a secondary blob cache by configuring `secondary_cache` in LRUCacheOptions.
 * Charge memory usage of blob cache when the backing cache of the blob cache and the block cache are different. If an operation reserving memory for blob cache exceeds the avaible space left in the block cache at some point (i.e, causing a cache full under `LRUCacheOptions::strict_capacity_limit` = true), creation will fail with `Status::MemoryLimit()`. To opt in this feature, enable charging `CacheEntryRole::kBlobCache` in `BlockBasedTableOptions::cache_usage_options`.
 * Improve subcompaction range partition so that it is likely to be more even. More evenly distribution of subcompaction will improve compaction throughput for some workloads. All input files' index blocks to sample some anchor key points from which we pick positions to partition the input range. This would introduce some CPU overhead in compaction preparation phase, if subcompaction is enabled, but it should be a small fraction of the CPU usage of the whole compaction process. This also brings a behavier change: subcompaction number is much more likely to maxed out than before.
+* Add CompactionPri::kRoundRobin, a compaction picking mode that cycles through all the files with a compact cursor in a round-robin manner. This feature is available since 7.5.
 
 ### Public API changes
 * Removed Customizable support for RateLimiter and removed its CreateFromString() and Type() functions.