Add utility for config loading

[einarmo]

Just a simple utility class containing code for fetching configs from CDF. It's maybe a bit early for this, since I still don't have a perfectly clear idea of how it's going to be used, but most of the logic here makes sense in general, and is a foundation for future work.

[codecov]

Codecov Report

Attention: Patch coverage is 85.18519% with 24 lines in your changes missing coverage. Please review.

Project coverage is 78.16%. Comparing base (bf8116d) to head (76aabe9).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...ractorUtils/Unstable/Configuration/ConfigSource.cs	83.56%	17 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #521      +/-   ##
==========================================
+ Coverage   78.08%   78.16%   +0.07%     
==========================================
  Files         122      123       +1     
  Lines       11387    11541     +154     
  Branches     1728     1748      +20     
==========================================
+ Hits         8892     9021     +129     
- Misses       1793     1811      +18     
- Partials      702      709       +7     

Files with missing lines	Coverage Δ
Cognite.Config/Configuration.cs	87.32% <100.00%> (+0.55%)	⬆️
...xtractorUtils/Unstable/DestinationUtilsUnstable.cs	64.07% <100.00%> (+0.43%)	⬆️
...ractorUtils/Unstable/Configuration/ConfigSource.cs	83.56% <83.56%> (ø)

... and 2 files with indirect coverage changes

[ozangoktan]

LGTM!