Use ParseLiveQuery Subscription as a SwiftUI view model

[cbaker6]

Adds support to use a ParseLiveQuery subscription as a VM. Once more people start using the SDK, this will probably be a highly sought after feature.

ParseLiveQuery and its ability to subscribe to events is suited to be a great candidate for SwiftUI updates or serve as a publisher of data in general to allow updates to views. The original Subscription, now renamed to SubscriptionCallback was a spin on the original Subscription in ParseLiveQuery-iOS. The new Subscription and the original essentially behave in a similar manner except the original was designed before property wrappers and before SwiftUI.

The change allows devs a different way from the objective-c SDK when accessing Parse data.

1. Use a traditional query find (pull) to get the original objects to display in your SwiftUI view.
2. Use a ParseLiveQuery Subscription as a view model (VM) for any subsequent updates in your SwiftUI view.

This update is "slightly" breaking as the original Subscription has been renamed to SubscriptionCallback. Both still have properties accessible directly from any Query. For example if you have var query = GameScore.query("score" > 9). Then:

1. Subscription - let subscription = query.subscribe
2. SubscriptionCallback - let subscription = query.subscribeCallback

[codecov]

Codecov Report

Merging #65 (986920c) into main (80802c5) will increase coverage by 0.15%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
+ Coverage   77.95%   78.11%   +0.15%     
==========================================
  Files          51       51              
  Lines        4578     4614      +36     
==========================================
+ Hits         3569     3604      +35     
- Misses       1009     1010       +1     

Impacted Files	Coverage Δ
Sources/ParseSwift/LiveQuery/ParseLiveQuery.swift	74.61% <0.00%> (-0.13%)	⬇️
Sources/ParseSwift/LiveQuery/Subscription.swift	75.94% <94.11%> (+12.68%)	⬆️
Sources/ParseSwift/Objects/ParseUser.swift	75.04% <0.00%> (+0.17%)	⬆️
Sources/ParseSwift/Objects/ParseObject.swift	76.31% <0.00%> (+0.29%)	⬆️

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[cbaker6]

@TomWFox I added docs to the "new" Subscription. Can you review them?

[TomWFox]

Just one . 😅

LGTM 🚀