CodeGen from PR 14590 in Azure/azure-rest-api-specs

SignalR new Api version 2021-06-01-preview (#14590)

* Init SignalR new Preview API version 2021-06-01-preview. Copy from 2021-04-01-preview

* init 2021-06-01-preview

* revert unneeded change

* revert unneeded change

* add property

* rename FQDN to Fqdn

* add missing example

* update authtype

* revert two properties

Co-authored-by: Binjie Qian <biqian@microsoft.com>