feat: Offline mode

[vdkdamian]

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New Pull Request Checklist

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

Issue Description

This adds the possibility to use ParseSwift with offline mode. Objects will be stored on device if needed and can be fetched when internet connection is back.

Closes: https://github.com/parse-community/Parse-Swift/issues/429

Approach

I will add playground examples on how to use it.

TODOs before merging

• [ ] Test
• [x] Linting
• [x] Add tests
• [ ] Add entry to changelog
• [x] Add changes to documentation (guides, repository pages, in-code descriptions)
• [x] Add playground examples

[parse-github-assistant[bot]]

Thanks for opening this pull request!

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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 83.59942% with 113 lines in your changes are missing coverage. Please review.

Project coverage is 87.53%. Comparing base (3d4bb13) to head (e34dd82).

Files	Patch %	Lines
Sources/ParseSwift/Storage/LocalStorage.swift	89.22%	46 Missing :warning:
Sources/ParseSwift/Types/Query.swift	68.65%	42 Missing :warning:
Sources/ParseSwift/Objects/ParseObject.swift	61.11%	21 Missing :warning:
Sources/ParseSwift/Extensions/URLSession.swift	80.00%	2 Missing :warning:
Sources/ParseSwift/Storage/ParseFileManager.swift	90.47%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #435      +/-   ##
==========================================
- Coverage   90.37%   87.53%   -2.84%     
==========================================
  Files         161      162       +1     
  Lines       16267    16929     +662     
==========================================
+ Hits        14701    14819     +118     
- Misses       1566     2110     +544     

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[vdkdamian]

I reached the limit of what I can cover for CodeCov