machinelearningservices has duplicate "x-ms-discriminator-value": "uri_folder" with DataVersionBase

The `x-ms-discriminator-value`s need to be unique under DataVersionBase.

``` json
"DataImport": {
"type": "object",
"allOf": [
{
"$ref": "#/definitions/DataVersionBase"
}
],
"properties": {
"assetName": {
"description": "Name of the asset for data import job to create",
"type": "string",
"x-nullable": true
},
"source": {
"description": "Source data of the asset to import from",
"$ref": "#/definitions/DataImportSource",
"x-nullable": true
}
},
"x-ms-discriminator-value": "uri_folder",
"additionalProperties": false
},

"UriFolderDataVersion": {
"description": "uri-folder data version entity",
"type": "object",
"allOf": [
{
"$ref": "#/definitions/DataVersionBase"
}
],
"x-ms-discriminator-value": "uri_folder",
"additionalProperties": false
},
```

Locate the machinelearningservices schema definitions for DataImport, UriFolderDataVersion, and DataVersionBase shown in the issue. Compare their x-ms-discriminator-value entries, determine the intended unique values, and run the repository's relevant specification validation to confirm that no discriminator duplicates remain.

Written by the indexing model from the issue text.