Add schema support for appsettings.json

[JamesNK]

Fixes #4279

[codecov]

Codecov Report

Merging #4280 (6c6a1a4) into master (4b1c180) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4280   +/-   ##
=======================================
  Coverage   85.99%   85.99%           
=======================================
  Files          60       60           
  Lines        1857     1857           
  Branches      215      215           
=======================================
  Hits         1597     1597           
  Misses        200      200           
  Partials       60       60           

Flag	Coverage Δ
integration	100.00% <ø> (ø)
unit	85.99% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4b1c180...6c6a1a4. Read the comment docs.

[JoeRobich]

@JamesNK Thanks!