Add changelog for Crashlytics and Perf integrating with Sessions (#5123)

* Add changelog for Crashlytics and Perf integrating with Sessions

* Changelog entry as [feature] not [added]

Author: mrober

firebase-crashlytics/CHANGELOG.md

@@ -1,5 +1,7 @@
 # Unreleased
 
+* [feature] Integrated with Firebase sessions library to enable upcoming features related to
+  session-based crash metrics.
 
 # 18.3.7
 * [feature] Added collection of version control information generated by the
@@ -490,4 +492,3 @@ The following release notes describe changes in the new SDK.
  from your `AndroidManifest.xml` file.
  * [removed] The `fabric.properties` and `crashlytics.properties` files are no
  longer supported. Remove them from your app.
-

firebase-perf/CHANGELOG.md

@@ -1,5 +1,8 @@
 # Unreleased
 
+* [feature] Integrated with Firebase sessions library to enable upcoming features related to
+  session-based performance metrics.
+
 # 20.3.3
 * [fixed] Fixed app start trace creation where some measured time could be NULL (#4730).
 * [changed] Adjusted default behavior when remote config fetch fails.