Persist current SDK version for migrating between versions

[cbaker6]

• Add ParseVersion and store to Keychain
• Add testcases
• Add playground example
• Add changelog
• Prepare for new release

[codecov]

Codecov Report

Merging #182 (1af26af) into main (5ee216f) will increase coverage by 0.20%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #182      +/-   ##
==========================================
+ Coverage   82.25%   82.45%   +0.20%     
==========================================
  Files          71       72       +1     
  Lines        6649     6726      +77     
==========================================
+ Hits         5469     5546      +77     
  Misses       1180     1180              

Impacted Files	Coverage Δ
Sources/ParseSwift/Storage/ParseStorage.swift	88.88% <ø> (ø)
Sources/ParseSwift/Parse.swift	100.00% <100.00%> (ø)
Sources/ParseSwift/Types/ParseVersion.swift	100.00% <100.00%> (ø)

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