[MOB-9747] FCM support

[evantk91]

🔹 Jira Ticket(s)

• MOB-9747

✏️ Description

This pull request introduces a config value, useFirebaseMessaging. This allows iOS apps to enable FCM to be used for notifications.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 10 lines in your changes missing coverage. Please review.

Project coverage is 68.98%. Comparing base (6e2fdec) to head (1ca866e).
Report is 861 commits behind head on master.

Files with missing lines	Patch %	Lines
swift-sdk/SDK/IterableAPI.swift	0.00%	5 Missing ⚠️
...-sdk/Internal/InternalIterableAppIntegration.swift	57.14%	3 Missing ⚠️
swift-sdk/Core/Constants.swift	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #906       +/-   ##
===========================================
- Coverage   85.19%   68.98%   -16.21%     
===========================================
  Files          91      104       +13     
  Lines        6301     7542     +1241     
===========================================
- Hits         5368     5203      -165     
- Misses        933     2339     +1406     

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