[PM-28177] Add feature flag for Send UI refresh (#6708)

Author: mcamirault

src/Core/Constants.cs

@@ -238,6 +238,7 @@ public static class FeatureFlagKeys
     public const string UseSdkPasswordGenerators = "pm-19976-use-sdk-password-generators";
     public const string UseChromiumImporter = "pm-23982-chromium-importer";
     public const string ChromiumImporterWithABE = "pm-25855-chromium-importer-abe";
+    public const string SendUIRefresh = "pm-28175-send-ui-refresh";
 
     /* Vault Team */
     public const string CipherKeyEncryption = "cipher-key-encryption";