[WIP][Android] Add breaking change docs for setting flags via the CLI in release mode

[camsim99]

Description of what this PR is changing or adding, and why:

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[flutter-website-bot]

Staged preview of the updated flutter.dev site (updated for commit 94e172e):

https://flutter-dev-230821--www-pr13796-cli-bc-bza14d47.web.app