iOS: add plugin manager

[nancywu1]

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[codecov]

Codecov Report

Attention: Patch coverage is 96.15385% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.76%. Comparing base (d2cd181) to head (8bb6f6a).
Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
ios/core/Sources/PluginManager.swift	96.55%	1 Missing ⚠️
...lugins/metrics/swiftui/Sources/MetricsPlugin.swift	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #603      +/-   ##
==========================================
- Coverage   89.77%   89.76%   -0.02%     
==========================================
  Files         331      332       +1     
  Lines       19904    19943      +39     
  Branches     1949     1949              
==========================================
+ Hits        17869    17902      +33     
- Misses       2021     2027       +6     
  Partials       14       14              

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