Correctly support scalar and other Serilog log property values when parsing to string

[stijnmoreels]

Describe the bug
When converting the Serilog values to Azure Application Insights models, we have a .ToDecentString method that takes in the Serilog log property value and returns the simple string representation of that value.
This works for simple values, but more complex values (like JSON values), this will result in escaped characters.

To Reproduce
Add a telemetry context to any logging extension method with a JSON value.

Expected behavior
The end-result Azure Application Insights telemetry value should contain the original JSON value (unescaped).

Additional context

• Current version (v2.3.0)
• Relates to RequestBody is logged as an escaped JSON string arcus.webapi#270