feat(ios)!: migrate to CDVAppDelegate and move logic to PushPlugin.m

[erisu]

Description

• Start using CDVAppDelegate instead of AppDelegate
• Move logic to PushPlugin.m.

Related Issue

Resolves #252
Resolves #172
Closes #186

Motivation and Context

• Follow Cordova standards
• Centralize plugin login

How Has This Been Tested?

• Tested APNS Payload drops

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[github-actions]

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