7.x only REST specification fixes (#56736)

Fixes for the REST specification specific to 7.x

* remove ignore "cat.thread_pool.json" and add the "" as valid option. #55984 deprecated this field since it these params here have no effect on this specific API
* remove ignore "indices.put_mapping.json" by adding the required / in the path to pass validation.

rest-api-spec/build.gradle

@@ -10,8 +10,3 @@ artifacts {
   restSpecs(new File(projectDir, "src/main/resources/rest-api-spec/api"))
   restTests(new File(projectDir, "src/main/resources/rest-api-spec/test"))
 }
-
-validateRestSpec {
-   ignore "cat.thread_pool.json"
-   ignore "indices.put_mapping.json"
-}

rest-api-spec/src/main/resources/rest-api-spec/api/cat.thread_pool.json

@@ -44,7 +44,7 @@
           "p"
         ],
         "deprecated":{
-          "version":"7.8.0",
+          "version":"7.7.0",
           "description":"Setting this value has no effect and will be removed from the specification."
         }
       },

rest-api-spec/src/main/resources/rest-api-spec/api/indices.put_mapping.json

@@ -127,7 +127,7 @@
           }
         },
         {
-          "path":"{index}/_mappings",
+          "path":"/{index}/_mappings",
           "methods":[
             "PUT",
             "POST"

rest-api-spec/src/main/resources/schema.json

@@ -201,7 +201,7 @@
                     "type": "array",
                     "items": {
                         "type": "string",
-                        "pattern": "^[a-zA-Z_]+$"
+                        "pattern": "^\\d*|[a-zA-Z_]+$"
                     },
                     "title": "Valid options when type is an enum"
                 },