[Feature Request] Add a custom JSon serializer for CredentialDescription in .NET 8+

[jmprieur]

Is your feature request related to a problem? Please describe.
When serializing CredentialsDescription instances, there is a lot of information that is not relevant. It would be good to have a Custom json serializer at least in .NET 8 (to avoid brining new dependencies in .NET 462, netstandard)

Describe the solution you'd like
Add a custom JSon serializer. the Write method would only write the right properties based on the value of the sourceType enumeration. Do not write the Id, do not write the Cache, the Certificate and Skip

Describe alternatives you've considered
Add to all target framwork, but it's really needed for tools (written in .NET 8+)