fix: Installation not saving to keychain correctly, returning nil instead

[cbaker6]

New Pull Request Checklist

• I am not disclosing a vulnerability.
• I am creating this PR in reference to an issue.

Issue Description

Installation not saving to the Keychain correctly, preventing the use of push notifications.

Related issue: #235

Approach

Save a BaseParseInstallation when initializing the SDK that can later be casted to the developers ParseInstallation.

When upgrading from previous versions of the SDK, this patch will attempt to fetch the installation from the Parse Server if it's available or else it will create a new one. If you added custom properties to your Installation you should call Installation.current?.fetch during SDK initialization to get the latest from the parse-server. Developers should also use cloud code/jobs to clean up any old installations that aren't being used anymore on the server.

TODOs before merging

• Add tests
• Add entry to changelog
• Add changes to read me
• Remove code duplication in spelling of variables
• Prepare for new release

[parse-github-assistant]

Thanks for opening this pull request!

• 🎉 We are excited about your hands-on contribution!

[cbaker6]

@lsmilek1 can you try out this branch and let me know if it works?

[codecov]

Codecov Report

Merging #236 (e9ba4ca) into main (1a30fb6) will decrease coverage by 0.12%.
The diff coverage is 93.45%.

❗ Current head e9ba4ca differs from pull request most recent head 0037836. Consider uploading reports for the commit 0037836 to get more accurate results

@@            Coverage Diff             @@
##             main     #236      +/-   ##
==========================================
- Coverage   83.73%   83.61%   -0.13%     
==========================================
  Files          78       78              
  Lines        7323     7360      +37     
==========================================
+ Hits         6132     6154      +22     
- Misses       1191     1206      +15     

Impacted Files	Coverage Δ
...es/ParseSwift/Internal/BaseParseInstallation.swift	33.33% <33.33%> (-66.67%)	⬇️
Sources/ParseSwift/Parse.swift	98.24% <96.77%> (-1.76%)	⬇️
Sources/ParseSwift/API/API.swift	98.31% <100.00%> (ø)
...Authentication/Protocols/ParseAuthentication.swift	74.46% <100.00%> (ø)
Sources/ParseSwift/LiveQuery/Messages.swift	100.00% <100.00%> (ø)
Sources/ParseSwift/LiveQuery/ParseLiveQuery.swift	74.38% <100.00%> (ø)
Sources/ParseSwift/Objects/ParseInstallation.swift	80.50% <100.00%> (+1.01%)	⬆️
Sources/ParseSwift/Objects/ParseUser.swift	82.84% <100.00%> (-0.15%)	⬇️
Sources/ParseSwift/Types/ParseConfig.swift	97.26% <100.00%> (ø)
Sources/ParseSwift/Internal/Data+hexString.swift	68.96% <0.00%> (-31.04%)	⬇️
... and 4 more

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[lsmilek1]

The problem was solved, now I get installation always. Thank you!