File service is not ingesting additional metadata

Old Implementation - we have created fixed set of schema for extension properties block and user not able to send additional metadata while posting metadata thought POST endpoint.

Changes - Updated model that accept addition metadata through extensionProperties. example - (NewKey and NewValue added as addition metadata)

"ExtensionProperties": {
           "Classification": "Raw File",
           "newKey" :"newValue",
           "Description": "An text further describing this file example.",
           "ExternalIds": [
               "string"
           ],
           "FileDateCreated": {},
           "FileDateModified": {},
}

MR - !157 (merged)