[ReleasePR apimanagement] APIM: improve developer portal operations docs (#1596)

Create to sync Azure/azure-rest-api-specs#13941
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/master...AzureSDKAutomation:sdkAuto/apimanagement?expand=1)

Author: msftbot[bot]

schemas/2021-01-01-preview/Microsoft.ApiManagement.json

@@ -213,7 +213,7 @@
               "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
             }
           ],
-          "description": "Api Create or Update Properties."
+          "description": "API Create or Update Properties."
         },
         "resources": {
           "type": "array",
@@ -2552,12 +2552,12 @@
           "type": "string",
           "minLength": 1,
           "maxLength": 100,
-          "description": "Describes the Revision of the Api. If no value is provided, default revision 1 is created"
+          "description": "Describes the revision of the API. If no value is provided, default revision 1 is created"
         },
         "apiRevisionDescription": {
           "type": "string",
           "maxLength": 256,
-          "description": "Description of the Api Revision."
+          "description": "Description of the API Revision."
         },
         "apiType": {
           "oneOf": [
@@ -2573,17 +2573,17 @@
               "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
             }
           ],
-          "description": "Type of Api to create. \n * `http` creates a REST API \n * `soap` creates a SOAP pass-through API  \n * `websocket` creates websocket API."
+          "description": "Type of API to create. \n * `http` creates a REST API \n * `soap` creates a SOAP pass-through API  \n * `websocket` creates websocket API."
         },
         "apiVersion": {
           "type": "string",
           "maxLength": 100,
-          "description": "Indicates the Version identifier of the API if the API is versioned"
+          "description": "Indicates the version identifier of the API if the API is versioned"
         },
         "apiVersionDescription": {
           "type": "string",
           "maxLength": 256,
-          "description": "Description of the Api Version."
+          "description": "Description of the API Version."
         },
         "apiVersionSet": {
           "oneOf": [
@@ -2774,7 +2774,7 @@
       "required": [
         "path"
       ],
-      "description": "Api Create or Update Properties."
+      "description": "API Create or Update Properties."
     },
     "ApiCreateOrUpdatePropertiesWsdlSelector": {
       "type": "object",
@@ -3450,7 +3450,7 @@
           "type": "string",
           "minLength": 1,
           "maxLength": 2000,
-          "description": "Management Uri of the Resource in External System. This url can be the Arm Resource Id of Logic Apps, Function Apps or Api Apps."
+          "description": "Management Uri of the Resource in External System. This url can be the Arm Resource Id of Logic Apps, Function Apps or API Apps."
         },
         "title": {
           "type": "string",
@@ -4576,7 +4576,7 @@
         },
         "secretIdentifier": {
           "type": "string",
-          "description": "Key vault secret identifier for fetching secret. Providing a versioned secret will prevent auto-refresh. This requires Api Management service to be configured with aka.ms/apimmsi"
+          "description": "Key vault secret identifier for fetching secret. Providing a versioned secret will prevent auto-refresh. This requires API Management service to be configured with aka.ms/apimmsi"
         }
       },
       "description": "Create keyVault contract details."
@@ -5024,7 +5024,7 @@
               "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
             }
           ],
-          "description": "Indicates if the Portal Revision is public."
+          "description": "Indicates if the portal's revision is public."
         }
       }
     },
@@ -5431,7 +5431,7 @@
               "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
             }
           ],
-          "description": "Api Create or Update Properties."
+          "description": "API Create or Update Properties."
         },
         "type": {
           "type": "string",