Add CHANGELOG for missing PR 6733 and 6651 (fragment generation compression)

Ref: #6733
Ref: #6651

Author: abernix

CHANGELOG.md

@@ -66,7 +66,17 @@ Unnecessary cache-control directives are created in cache-control header.  The r
 
 By [@bnjjj](https://github.com/bnjjj) in https://github.com/apollographql/router/pull/6543
 
+### Resolve regressions in fragment compression for certain operations ([PR #6651](https://github.com/apollographql/router/pull/6651))
 
+In v1.58.0 we introduced a new compression strategy for subgraph GraphQL operations to replace an older, more complicated algorithm.
+
+While we were able to validate improvements for a majority of cases, some regressions still surfaced.  To address this, we are extending it to compress more operations with the following outcomes:
+
+* The P99 overhead of running the new compression algorithm on the largest operations in our corpus is now just **10ms**
+* In case of _better_ compression, at P99 it shrinks the operations by **50Kb** when compared to the old algorithm
+* In case of _worse_ compression, at P99 it only adds an additional 108 _bytes_ compared to the old algorithm, which was an acceptable trade-off versus added complexity
+
+By [@dariuszkuc](https://github.com/dariuszkuc) in https://github.com/apollographql/router/pull/6651
 
 # [1.60.0] - 2025-02-05