Fix optional parameters design

[scottinet]

⚠️ depends on #13

Description

After a long and heated debate, we adopted a different and more idiomatic way of passing optional parameters to methods.

It goes like this:

• as long as optional arguments are local to the called function (not passed around, not saved, discarded once the function is finished): the options are to be passed as default arguments. It doesn't matter if there are many optional arguments, as C# allows named parameters
• if optional arguments needs to be passed around or kept after the function finishes, then they must be put in a dedicated class

Examples:

• the function responsible of the document:update API (DocumentController.UpdateAsync) now takes both a bool waitForRefresh and a int? retryOnConflict optional arguments
• search options needs to be kept after DocumentController.SearchAsync finishes, as it is passed to the SearchResult instances that are created afterward to handle search pagination: so the SearchOptions object is unchanged

[codecov]

Codecov Report

Merging #14 into 0-dev will increase coverage by 26.79%.
The diff coverage is 38.8%.

@@            Coverage Diff             @@
##           0-dev      #14       +/-   ##
==========================================
+ Coverage   3.45%   30.25%   +26.79%     
==========================================
  Files         19       17        -2     
  Lines        898      876       -22     
  Branches     107      105        -2     
==========================================
+ Hits          31      265      +234     
+ Misses       866      610      -256     
  Partials       1        1

Impacted Files	Coverage Δ
Kuzzle/Kuzzle.cs	0% <0%> (ø)	⬆️
Kuzzle/API/Controllers/DocumentController.cs	0% <0%> (ø)	⬆️
Kuzzle/API/Options/SearchOptions.cs	100% <100%> (+100%)	⬆️
Kuzzle/API/Controllers/CollectionController.cs	100% <100%> (+100%)	⬆️
Kuzzle/API/Controllers/AuthController.cs	100% <100%> (+84.73%)	⬆️
Kuzzle/API/DataObjects/SearchResults.cs	26.47% <0%> (+26.47%)	⬆️

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