feat: summary changes

Signed-off-by: Manan Gupta <[email protected]>

changelog/21.0/21.0.0/summary.md

@@ -11,6 +11,7 @@
   - **[Traffic Mirroring](#traffic-mirroring)**
   - **[New VTGate Shutdown Behavior](#new-vtgate-shutdown-behavior)**
   - **[Tablet Throttler: Multi-Metric support](#tablet-throttler)**
+  - **[Allow Cross Cell Promotion in PRS](#allow-cross-cell)**
 
 ## <a id="major-changes"/>Major Changes
 
@@ -96,3 +97,8 @@ Each metric has a factory threshold which can be overridden by the `UpdateThrott
 The throttler also supports the catch-all `"all"` app name, and it is thus possible to assign metrics to _all_ apps. Explicit app to metric assignments will override the catch-all configuration.
 
 Metrics are assigned a default _scope_, which could be `self` (isolated to the tablet) or `shard` (max, aka _worst_ value among shard tablets). It is further possible to require a different scope for each metric.
+
+### <a id="allow-cross-cell"/>Allow Cross Cell Promotion in PRS
+Up until now if the users wanted to promote a replica in a different cell than the current primary using `PlannedReparentShard`, they had to specify the new primary with the `--new-primary` flag.
+
+We have now added a new flag `--allow-cross-cell-promotion` that lets `PlannedReparentShard` choose a primary in a different cell even if no new primary is provided explicitly.