Add devcontainer configuration

[Strift]

Pull Request

This PR adds a devcontainer configuration to allow development locally without needing to install Java.

Compared to the existing docker-compose configuration, it allows VS code to interact with Java, and run gradle from the IDE.

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Please check if your PR fulfills the following requirements:

• Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
• Have you read the contributing guidelines?
• Have you made sure that the title is accurate and descriptive of the changes?

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