docs: align Flutter native dependency versions for CNAME updates

[denischilik]

Summary

• pin Android native dependencies to com.mparticle:android-core:5.79.0 and com.mparticle:android-rokt-kit:5.79.0 in plugin/example Gradle configs and setup docs
• bump iOS podspec dependency guidance to mParticle-Apple-SDK ~> 9.2
• add native CNAME initialization examples in README for Android (NetworkOptions.withNetworkOptions) and iOS (MPNetworkOptions.customBaseURL)

Test plan

• Documentation-only verification: review README.md, CHANGELOG.md, and ios/mparticle_flutter_sdk.podspec for version consistency
• Android build smoke check in example app with pinned dependency versions
• iOS pod install smoke check with mParticle-Apple-SDK ~> 9.2

[cursor]

PR Summary

Medium Risk
Medium risk because it changes shipped native dependency versions (Android Gradle and iOS podspec), which can affect build compatibility and runtime behavior even though no Dart/plugin logic changes.

Overview
Updates native dependency guidance and defaults to match newer SDK versions and support CNAME routing.

Pins Android dependencies to com.mparticle:android-core:5.79.0 (and android-rokt-kit:5.79.0 where applicable) in the README and in the plugin/example Gradle builds, and bumps the iOS CocoaPods dependency in mparticle_flutter_sdk.podspec/docs from mParticle-Apple-SDK ~> 9.1 to ~> 9.2.

Adds optional CNAME initialization examples: Android via NetworkOptions.withNetworkOptions(...) and iOS via MPNetworkOptions.customBaseURL, and records these changes in CHANGELOG.md.

^{Reviewed by Cursor Bugbot for commit 4faeef9. Bugbot is set up for automated code reviews on this repo. Configure here.}

[thomson-t]

Please add a comment to explain this is an optional configuration or better move the CNAME config to it's own section in the docs.

[denischilik]

Done