Applies to & new values

By default when visiting this page a user is shown the version that relates to the latest version of the .net framework (4.7.2), which is the first version to include EphemeralKeySet. This is a bit confusing as the "Applies to" section calls out frameworks going back quite some time.

Given the newness of this enum value, it might be helpful to call out the new/exception case, as anyone not developing against 4.7.2 may be confused as to why they do not see it when developing.

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#### Document Details

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* ID: 2503df85-08d1-0e2b-c0ac-f0b0a26f5158
* Version Independent ID: 3f362403-2677-9750-42ee-c032e62bc6d6
* Content: [X509KeyStorageFlags Enum (System.Security.Cryptography.X509Certificates)](https://docs.microsoft.com/en-us/dotnet/api/system.security.cryptography.x509certificates.x509keystorageflags?view=netframework-4.7.2)
* Content Source: [xml/System.Security.Cryptography.X509Certificates/X509KeyStorageFlags.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Security.Cryptography.X509Certificates/X509KeyStorageFlags.xml)
* Product: **dotnet-api**
* GitHub Login: @mairaw
* Microsoft Alias: **mairaw**