Add DevContainer

[wsciaroni]

This PR adds a dev container configuration to streamline the development environment setup for contributors.

Benefits

• Simplifies setup for new developers.
• Ensures a consistent environment for all.
• Reduces onboarding friction.
• Pre-configured with necessary tools and extensions (Java, Gradle, Android SDK, etc.).

Documentation Note

Since the developer of KV4P does not regularly use devcontainers, the documentation should mention this devcontainer is community-supported and may require adjustments depending on individual needs and setups. It is not officially maintained by the project.

How to use:

• Install the Dev Containers extension in VS Code.
• Open the project in VS Code.
• Reopen the project in the container when prompted.
• This change aims to improve the developer experience and encourage contributions.

[VanceVagell]

Thanks for this. As you noted, I don't use this workflow but it doesn't seem to interfere with using Android Studio directly and if it helps others get up and running, awesome!