fix: PBMod updated according to Table 5 of ESS-0038258 revision 6.

init/databuffer-ess.json

 {
-  "ProtNum": 5,
+  "ProtNum": 6,
   "ProtVer": 1,
   "PBState": {
     "None": {
@@ -48,6 +48,10 @@
       "id": 40,
       "description": "To perform an initial RF test with a longer pulse."
     },
+    "StabilityTest": {
+      "id": 50,
+      "description": "To be used mostly for beam stability test."
+    },
     "SlowCommissioning": {
       "id": 60,
       "description": "Very short pulse planned to be used used during Normal Conducting Linac commissioning. It would allow installation of the rest of the Linac in parallel to Beam Commissioning."