Certain NIC dns settings should be marked read-only

Attempting to set `internalDomainNameSuffix` or `internalFqdn` for a PUT operation on a NIC's DNS settings results in the value being ignored and an automatic one being created. These parameters should be marked as readonly in Swagger since they cannot be set or changed.

See issue:
https://github.com/Azure/azure-cli/issues/6243

Search the Azure REST API specifications for the NIC DNS settings containing internalDomainNameSuffix and internalFqdn, then inspect their Swagger/OpenAPI definitions. Confirm how read-only properties are represented and mark both parameters accordingly; done means PUT operations no longer describe them as settable and the specification reflects the reported behavior.

Written by the indexing model from the issue text.