Docker build image and devcontainer config

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Add two docker files to the repository to enable:

• Containerised builds for Android, and
• Containerised development via devcontainer

NOTE: There are known issues with building this repository using docker on ARM-based systems (e.g. M-series Macs, Raspberry Pi):

• linux/amd64: Dart VM emulation on M1 Mac fails
• linux/arm64: Android APK build fails due to dependencies limiting the versions of the Dart SDK, Android Gradle plugin, and Gradle build tools. See the Gradle Compatibility Matrix

Usage

Use the following commands to build locally on x86 systems using Docker:

sh .docker/build_apk_release.sh

To build in GitHub Codespaces open a terminal and run:

flutter build apk --release

In both instances, the apk file should appear in build/app/outputs/flutter-apk/app-release.apk

Docker image source: Cirrus Labs Android SDK Images