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
Moderate risk because it bumps/pins underlying native SDK dependency versions, which can affect build resolution and runtime behavior despite being largely documentation/config updates.

Overview
Updates setup guidance and sample code to support CNAME routing by configuring a custom base URL (NetworkOptions.withNetworkOptions(...) on Android and MPNetworkOptions.customBaseURL on iOS).

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

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