no available type checker for linked service properties

originally opened in https://github.com/Azure/azure-sdk-for-python/issues/31975

swagger definition: https://github.com/Azure/azure-rest-api-specs/blob/main/specification/datafactory/resource-manager/Microsoft.DataFactory/stable/2018-06-01/entityTypes/LinkedService.json#L6707-L6709

Type checker defined here didn't work as expected. Properties can still be passed with value in any types other than `string`.

For example, as the log snippet shows, `newClusterNumOfWorker` can be passed with an `integer` though expected a `string`.
```
Request body:
{"properties": {"type": "AzureDatabricks", "typeProperties": {"domain": "https://adb-xxxxxxxxxxxxxx.x.azuredatabricks.net", "newClusterVersion": "13.3.x-scala2.12", "newClusterNumOfWorker": 2, "newClusterNodeType": "Standard_DS3_v2"}}}
```

**Expected behavior**
Type checker for type properties of linked service should be updated to be able to restrict the properties' value in `string` format.

Start with specification/datafactory/resource-manager/Microsoft.DataFactory/stable/2018-06-01/entityTypes/LinkedService.json at lines 6707-6709, then trace the type checker used for linked-service type properties. Done means values for these properties are restricted to strings, including rejecting the integer shown in the request example.

Written by the indexing model from the issue text.