Update .NET Core 3.1 example

[Crossbow78]

• Apply ILogger, IOptions, IHostedService patterns to .NET Core 3.1 example
• Trim unnecessary bits
• Enforce 'Out-of-process' hosting model or the example will not run correctly
• Consolidated line-ending in two files

[codecov]

Codecov Report

Merging #514 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #514   +/-   ##
=======================================
  Coverage   76.00%   76.00%           
=======================================
  Files         135      135           
  Lines        5248     5248           
  Branches      517      517           
=======================================
  Hits         3989     3989           
  Misses       1105     1105           
  Partials      154      154           

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[StefH]

@Crossbow78 Thank you very much!