Remove hard dependency on Newtonsoft serialization

My understanding is Hangfire depends on Newtonsoft to serialize jobs and the objects being passed through them.

We'd like to utilize System.Text.Json as this is one of the last dependencies we have that requires Newtonsoft (and thus a lot of extra decoration/overhead).

Thanks

Start by tracing where Hangfire serializes jobs and their arguments, then identify the project-wide Newtonsoft dependency and the compatibility requirements for System.Text.Json. Done means job serialization works without a hard Newtonsoft dependency, including existing supported job payloads; the issue names no files or tests to run.

Written by the indexing model from the issue text.