Future proof SDK by always sending clientVersion header

[cbaker6]

These changes will proof the SDK by making it easier for future additions.

• Always send clientVersion header with all API calls. This allows the server to handle different versions of the client SDK in particular ways
• Add PATCH to API for future use
• Fix context playground example
• Test changes in playground with real server to ensure everything still works
• Add entry to changelog

[codecov]

Codecov Report

Merging #146 (aab6eec) into main (608a69f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #146   +/-   ##
=======================================
  Coverage   81.51%   81.52%           
=======================================
  Files          68       68           
  Lines        6384     6387    +3     
=======================================
+ Hits         5204     5207    +3     
  Misses       1180     1180           

Impacted Files	Coverage Δ
Sources/ParseSwift/API/API+Commands.swift	79.55% <100.00%> (ø)
Sources/ParseSwift/API/API.swift	98.23% <100.00%> (+0.04%)	⬆️
Sources/ParseSwift/Objects/ParseInstallation.swift	78.62% <100.00%> (ø)
Sources/ParseSwift/Objects/ParseObject.swift	77.00% <0.00%> (-0.54%)	⬇️
Sources/ParseSwift/Coding/ParseEncoder.swift	75.16% <0.00%> (+0.32%)	⬆️

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