Feature Request: Add Support for System.Text.Json in SlackNet

[huoshan12345]

Hi,

Thank you for maintaining SlackNet and making it an excellent library.
Currently, SlackNet uses Newtonsoft.Json for JSON serialization and deserialization.
I would like to request adding support for System.Text.Json in SlackNet.

Suggested Implementation:

• Introduce a mechanism (e.g., an interface or factory) that allows developers to plug in a custom JSON serializer.
• Provide a default implementation for both Newtonsoft.Json and System.Text.Json.

Thank you for considering this feature request. Please let me know if I can help with further details or testing!

[soxtoby]

Hi @huoshan12345. At some point I do want to switch to System.Text.Json, but it won't be straightforward.

SlackNet makes a lot of customizations to the serialization in order to support Slack's serialization standards, which would all need to be re-implemented with the STJ API.

Additionally, many classes rely on Newtonsoft.Json's attributes, and types like JObject, which have equivalents in STJ, but which would make it difficult, if not impossible, to support multiple serialization libraries.