[changelog] v1.4.0 updates (#3937)

CHANGELOG.md

@@ -1,9 +1,20 @@
 # Changelog
 
-# Upcoming
+# 1.4.0
+
+## Features
+- **M3Query**: Add write endpoint support for M3-Map-Tags-JSON header in InfluxDB path ([#3816](https://github.com/m3db/m3/pull/3816))
+- **M3Query**: Add support for `last_over_time` in M3Query engine ([#3884](https://github.com/m3db/m3/pull/3884))
+- **M3Aggregator**: Add p75/p25 as aggregation options ([#3867](https://github.com/m3db/m3/pull/3867))
+
+## Bug Fixes
+- **M3DB**: Fix M3TSZ to be deterministic when encoding high precision values ([3872](https://github.com/m3db/m3/pull/3872))
+- **M3DB**: Gracefully handle reads including documents with stale index state ([3905](https://github.com/m3db/m3/pull/3905))
 
 ## Performance
-- **M3Aggregator**: Rework close and remove `persitFlushTimesEvery` semantics in leader flushing in favour of always persisting shard flush times on a successful flush for optimized graceful failovers. ([#3890](https://github.com/m3db/m3/pull/3890))
+- **M3Aggregator**: Rework close and remove `persitFlushTimesEvery` semantics in leader flushing in favour of always persisting shard flush times on a successful flush for optimized graceful failovers ([#3890](https://github.com/m3db/m3/pull/3890))
+- **M3DB**: Optimize `filesetFiles` function during bootstrapping for namespaces with long retentions to prevent CPU spikes ([#3900](https://github.com/m3db/m3/pull/3900))
+- **M3DB**: Avoid loading blocks in memory for namespaces with snapshots disabled during bootstrapping to reduce memory usage ([#3919](https://github.com/m3db/m3/pull/3919))
 
 # 1.3.0