[Appservice] In operation WebApps_CreateOrUpdate invalid read_only column is defined in extendedLocation

Our customer found that when trying to create an App Service web app that uses a custom location, we can not serialize the `type` column in `extendedLocation` definition.

After investigation we found that there is a `read_only` limitation for field `type` so we can't feed data in client side. After removing this limitation and the request could be handled correctly in server side.

Swagger code link: https://github.com/Azure/azure-rest-api-specs/blob/bb9f1204f9a337404ff7e7b73b4c7b4ddde7f8f1/specification/web/resource-manager/Microsoft.Web/stable/2021-03-01/CommonDefinitions.json#L1372-L1375

SDK issue link: https://github.com/Azure/azure-sdk-for-js/issues/20570

Start at CommonDefinitions.json around lines 1372-1375 and inspect the extendedLocation type definition, then review the linked Azure SDK for JS issue. Remove the read_only limitation from the type field and verify that WebApps_CreateOrUpdate can serialize a custom location with extendedLocation.type.

Written by the indexing model from the issue text.