CodeGen from PR 15289 in Azure/azure-rest-api-specs

Add MySQL swagger files for GA stable version 2021-05-01 (#15289)

* Copy the existing version 2021-05-01-preview into stable directory 2021-05-01

* Update api-version

* Update readme

* Fix go readme

* Correct the api-version in examples

* Remove server.identity as is was currently not supported

* Update readme to support multi API

* change the default package to single server in readme

schemas/2017-12-01/Microsoft.DBforMySQL.json

@@ -693,7 +693,7 @@
       "properties": {
         "administratorLogin": {
           "type": "string",
-          "description": "The administrator's login name of a server. Can only be specified when the server is being created (and is required for creation)."
+          "description": "The administrator's login name of a server. Can only be specified when the server is being created (and is required for creation). The login name is required when updating password."
         },
         "administratorLoginPassword": {
           "type": "string",