Advise use of a single options instance in a custom converter

[tdykstra]

See dotnet/runtime#40072 and dotnet/runtime#42167 (comment)

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• ID: 5de37d79-751f-e372-e866-efde28f4908c
• Version Independent ID: 678c4f23-764a-7ccd-0d6d-159a30957477
• Content: How to write custom converters for JSON serialization - .NET
• Content Source: docs/standard/serialization/system-text-json-converters-how-to.md
• Product: dotnet
• GitHub Login: @tdykstra
• Microsoft Alias: tdykstra

[layomia]

FWI this applies to all usages of JsonSerializerOptions (including at the root calls to the serializer), not just in custom converters.

Another thing to avoid is passing numerous dynamically generated types to the serializer as this can lead to an OutOfMemoryException. An example of this can be found here - dotnet/aspnetcore#24230.