Enable replication separately from namespace replication (#8658)

## What changed?
- Add a new flag that controls whether clusters setup replication
streams to each other
- Feature flag to gate the new flag for compatibility
- Functional test to vet the changes

## Why?
Optimization to avoid excessive network activity when we only want
namespace replication.

## How did you test it?
- [x] built
- [x] run locally and tested manually
- [x] covered by existing tests
- [ ] added new unit test(s)
- [x] added new functional test(s)

---------

Co-authored-by: Claude <noreply@anthropic.com>

service/history/configs/config.go

@@ -11,8 +11,9 @@ import (
 type Config struct {
 	NumberOfShards int32
 
-	EnableReplicationStream dynamicconfig.BoolPropertyFn
-	HistoryReplicationDLQV2 dynamicconfig.BoolPropertyFn
+	EnableReplicationStream             dynamicconfig.BoolPropertyFn
+	EnableSeparateReplicationEnableFlag dynamicconfig.BoolPropertyFn
+	HistoryReplicationDLQV2             dynamicconfig.BoolPropertyFn
 
 	RPS                                         dynamicconfig.IntPropertyFn
 	OperatorRPSRatio                            dynamicconfig.FloatPropertyFn
@@ -403,8 +404,9 @@ func NewConfig(
 	cfg := &Config{
 		NumberOfShards: numberOfShards,
 
-		EnableReplicationStream: dynamicconfig.EnableReplicationStream.Get(dc),
-		HistoryReplicationDLQV2: dynamicconfig.EnableHistoryReplicationDLQV2.Get(dc),
+		EnableReplicationStream:             dynamicconfig.EnableReplicationStream.Get(dc),
+		EnableSeparateReplicationEnableFlag: dynamicconfig.EnableSeparateReplicationEnableFlag.Get(dc),
+		HistoryReplicationDLQV2:             dynamicconfig.EnableHistoryReplicationDLQV2.Get(dc),
 
 		RPS:                                  dynamicconfig.HistoryRPS.Get(dc),
 		OperatorRPSRatio:                     dynamicconfig.OperatorRPSRatio.Get(dc),