[ML] Updates visiblity of validate API (#81061) (#81109)

Author: lcawl

rest-api-spec/src/main/resources/rest-api-spec/api/ml.validate.json

@@ -5,7 +5,7 @@
       "description":"Validates an anomaly detection job."
     },
     "stability":"stable",
-    "visibility":"public",
+    "visibility":"private",
     "headers":{
       "accept": [ "application/json"],
       "content_type": ["application/json"]

rest-api-spec/src/main/resources/rest-api-spec/api/ml.validate_detector.json

@@ -5,7 +5,7 @@
       "description":"Validates an anomaly detection detector."
     },
     "stability":"stable",
-    "visibility":"public",
+    "visibility":"private",
     "headers":{
       "accept": [ "application/json"],
       "content_type": ["application/json"]