Steeltoe.Discovery.Eureka: Unrecognized DataCenterInfo.Name poisons entire registry fetch

An attacker who can control or influence the `DataCenterInfo.name` field in a Eureka instance registration — for example, by registering a malicious service instance with `name` set to `"Netflix"` — triggers an unhandled `ArgumentException` in `DataCenterInfo.FromJson` on any Steeltoe Eureka client that deserializes that registration [ref_id=1][ref_id=2]. The exception propagates through the entire registry deserialization chain and is swallowed by the periodic cache refresh task, leaving the local service registry permanently empty or stale [CWE-248]. In mixed Java/Spring and Steeltoe environments, the `Netflix` data center type is a standard value in the Java Eureka specification, so legitimate Java Eureka registrations can inadvertently poison the Steeltoe client's registry without any malicious intent [ref_id=1].

Both patches add an explicit check for the `"Netflix"` data center name in `DataCenterInfo.FromJson`, returning a valid `DataCenterInfo` object with `DataCenterName.Netflix` instead of throwing an exception [patch_id=6466813][patch_id=6466812]. For any unrecognized name, the method now returns `null` rather than throwing `ArgumentException` or `ArgumentOutOfRangeException`, which prevents the exception from propagating through the deserialization chain and corrupting the registry. The unit tests are updated accordingly: the `FromJson_Throws_Invalid` test is replaced with `FromJson_ReturnsNull_WhenInvalid`, and the `FromJson_Correct` test is parameterized to cover all three valid names (`MyOwn`, `Amazon`, `Netflix`) [patch_id=6466813][patch_id=6466812].