Add readonly attribute to earliest alert time field

salt/soc/soc_soc.yaml

@@ -1063,6 +1063,7 @@ soc:
               regex: '^(\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?Z)?$'
               regexFailureMessage: Expecting date in RFC3339 format (2026-09-24T00:00:00Z)
               global: True
+              readonly: True
               advanced: True
           tools:
             filterEventFields: