Use System.Net.Json instead of Newtonsoft.Json

[stijnmoreels]

Is your feature request related to a problem? Please describe.
We already used Microsoft's new System.Net.Json in the Web API template, but not in the Worker project templates. This due to the TCP health probe that still uses Newtonsoft.Json.

Describe the solution you'd like
Use Microsoft's new System.Net.Json package to serialize the health so that we can remove the Newtonsoft.Json dependency.

Additional context
arcus-azure/arcus.templates#484