fix a missing required and a description (#16421)

Author: giakas

specification/videoanalyzer/resource-manager/Microsoft.Media/preview/2021-11-01-preview/PipelineTopologies.json

@@ -388,6 +388,7 @@
       "type": "object",
       "required": [
         "@type",
+        "credentials",
         "url"
       ],
       "description": "Base class for endpoints."
@@ -856,7 +857,7 @@
         },
         "retentionPeriod": {
           "type": "string",
-          "description": "Video retention period indicates how long the video is kept in storage. Value must be specified in ISO8601 duration format (i.e. \"PT1D\" equals 1 day) and can vary between 1 day to 10 years, in 1 day increments. When absent (null), all video content is retained indefinitely. This property is only allowed for topologies where \"kind\" is set to \"live\"."
+          "description": "Video retention period indicates how long the video is kept in storage. Value must be specified in ISO8601 duration format (i.e. \"P1D\" equals 1 day) and can vary between 1 day to 10 years, in 1 day increments. When absent (null), all video content is retained indefinitely. This property is only allowed for topologies where \"kind\" is set to \"live\"."
         }
       },
       "type": "object",