[CIS-994] Fix the issue with receiving .didBecomeActive before connecting the client for the first time

[dmigach]

We spotted one additional case when it's possible for ChatClientUpdater.connect to be called before obtaining credentials:
#1218

It happens because we subscribe for notifications in ChatClient's init
Two fixes to prevent this:

1. Do not call ChatClientUpdater.connect if one of connect methods has not been called on ChatClient
2. Only listen to app state notifications in connected state, i.e. only subscribe when we connect and unsubscribe on disconnect

[Stream-iOS-Bot]

	1 Message
📖	There seems to be app changes but CHANGELOG wasn't modified. Please include an entry if the PR includes user-facing changes. You can find it at CHANGELOG.md.

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[codecov-commenter]

Codecov Report

Merging #1256 (f017c0a) into main (8dc565a) will decrease coverage by 0.12%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main    #1256      +/-   ##
==========================================
- Coverage   91.52%   91.40%   -0.13%     
==========================================
  Files         219      219              
  Lines        9400     9419      +19     
==========================================
+ Hits         8603     8609       +6     
- Misses        797      810      +13     

Flag	Coverage Δ
llc-tests	91.24% <50.00%> (-0.13%)	⬇️
llc-tests-ios12	88.09% <50.00%> (-0.12%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...Chat/WebSocketClient/BackgroundTaskScheduler.swift	43.75% <0.00%> (-21.97%)	⬇️
Sources/StreamChat/ChatClient.swift	94.39% <100.00%> (+0.70%)	⬆️

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