Add the mfa_serial profile property

Author: Austin Brooks

.changes/next-release/feature-AWSSDKforJavav2-dfce555.json

@@ -0,0 +1,5 @@
+{
+    "category": "AWS SDK for Java v2", 
+    "type": "feature", 
+    "description": "Add mfa_serial to ProfileProperty"
+}

core/profiles/src/main/java/software/amazon/awssdk/profiles/ProfileProperty.java

@@ -64,5 +64,10 @@ public final class ProfileProperty {
      */
     public static final String REGION = "region";
 
+    /**
+     * Property name for specifying the identification number of the MFA device
+     */
+    public static final String MFA_SERIAL = "mfa_serial";
+
     private ProfileProperty() {}
 }