fix(datastore): observeQuery snapshot on ready event

[lawmicha]

Issue #, if available: https://github.com/aws-amplify/amplify-ios/issues/1759

Description of changes: ObserveQuery is an API that provides a stream of data snapshots including the sync state. Roughly the behavior of the snapshot's emit intervals is this: The intervals adjusted based on the sync state, sending less frequent snapshots during the syncing process and more frequent snapshots after is synced. The issue, which was confirmed other platforms do not have and is expected, is that in between the last snapshot during sync and the first snapshot after sync is that the operation is missing a snapshot to indicate the sync state toggle. The customer impact is when there is an infrequent number item changes after syncing then the first snapshot after sync is delayed until there is a new item change, causing a large interval between the two snapshots.

The fix is to listen for the datastore ready event and emit a snapshot when receiving the ready event, which introduces the behavior of the missing snapshot.

Check points: (check or cross out if not relevant)

• [ ] Added new tests to cover change, if needed
• [ ] Build succeeds with all target using Swift Package Manager
• [ ] All unit tests pass
• [ ] All integration tests pass
• [ ] Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• [ ] Documentation update for the change if required
• [ ] PR title conforms to conventional commit style
• [ ] If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #2105 (3d7a733) into main (f0c3534) will decrease coverage by 0.01%. The diff coverage is 57.14%.

@@            Coverage Diff             @@
##             main    #2105      +/-   ##
==========================================
- Coverage   59.50%   59.48%   -0.02%     
==========================================
  Files         719      719              
  Lines       22561    22568       +7     
==========================================
  Hits        13425    13425              
- Misses       9136     9143       +7     

Flag	Coverage Δ
API_plugin_unit_test	62.47% <ø> (-0.10%)	:arrow_down:
AWSPluginsCore	70.29% <ø> (+0.07%)	:arrow_up:
Amplify	48.20% <ø> (-0.04%)	:arrow_down:
Analytics_plugin_unit_test	71.09% <ø> (ø)
Auth_plugin_unit_test	78.16% <ø> (ø)
DataStore_plugin_unit_test	75.60% <57.14%> (-0.04%)	:arrow_down:
Geo_plugin_unit_test	52.12% <ø> (ø)
Predictions_plugin_unit_test	26.81% <ø> (ø)
Storage_plugin_unit_test	58.04% <ø> (ø)

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Impacted Files	Coverage Δ
...gin/Subscribe/DataStoreObserveQueryOperation.swift	75.00% <57.14%> (+0.35%)	:arrow_up:
Amplify/Categories/Hub/HubFilter.swift	47.36% <0.00%> (-10.53%)	:arrow_down:
...lugin/Operation/AWSAPIOperation+APIOperation.swift	73.68% <0.00%> (-5.27%)	:arrow_down:
...oreCategoryPlugin/Sync/Support/Model+Compare.swift	68.75% <0.00%> (-3.13%)	:arrow_down:
...e/AWSPluginsCore/Auth/AWSAuthServiceBehavior.swift	87.50% <0.00%> (+12.50%)	:arrow_up:

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