Make AoT friendlier

[martincostello]

• Remove use of Refit to be AoT-friendlier. AoT is not supported though due to trimmer warnings from Newtonsoft.Json (via Alexa.NET) (see AoT Support? timheuer/alexa-skills-dotnet#262) and Microsoft.ApplicationInsights.
• Bump Newtonsoft.Json to 13.0.3.
• Group dependabot NuGet package updates for Polly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f1b4e57) 95.54% compared to head (0b6b01e) 96.98%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #964      +/-   ##
==========================================
+ Coverage   95.54%   96.98%   +1.43%     
==========================================
  Files          23       24       +1     
  Lines         539      497      -42     
  Branches       62       57       -5     
==========================================
- Hits          515      482      -33     
+ Misses         14        5       -9     
  Partials       10       10              

Flag	Coverage Δ
linux	?
macos	?
windows	96.98% <100.00%> (+1.43%)	⬆️

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