0.4.21 Nuget Release

[MattB-msft]

Added optional WebAPI support during login and solution import & export operations
Refactored ServiceClient and ConnectionService
Added new dependency on System.Text.Json, preparing for the removal of Newtonsoft dependency

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This discussion was created from the release 0.4.21 Nuget Release.

[rajyraman]

@MattB-msft - Can we start using System.Text.Json in plugins and workflows? Is it possible?

[MattB-msft]

Not yet.
Though we plan to have it available in the future, and allow your use of it before we have it as a standard lib.
and Yes, that is intentionally vague as we have not yet announce a few things :)

This change is in prep for removing Newtonsoft from the DV ServiceClient itself.