ExpressRoute Circuit Connection API returns "*****************" for AuthorizationKey when it's changed from a valid value to null

After tested, we found [ExpressRoute Circuit Connection](https://github.com/Azure/azure-rest-api-specs/blob/68c2d7c5e56c4c70e46d7158f19cdbf29dbdbfc4/specification/network/resource-manager/Microsoft.Network/stable/2020-11-01/expressRouteCircuit.json#L665)(aka: Global Reach Connection) API returns "*****************" AuthorizationKey when it's changed from a valid value to null. Seems the API behavior is weird. I assume it should be null. After confirmed with service team, they will handle this issue.

The issue points to specification/network/resource-manager/Microsoft.Network/stable/2020-11-01/expressRouteCircuit.json around the ExpressRoute Circuit Connection definition. Read that definition first and confirm the expected null behavior with the service team; the issue says they will handle the API behavior, so no repository change or completion test is identified.

Written by the indexing model from the issue text.