Allow unauthenticated access to /live on Backend2Backend REST API

[phfeustel]

Motivation When running the OpenEMS backend in (docker) containers and/or connect them via (cloud) load balancers, it is handy to have an easy to call liveness probe which does not need any authentication.

Side note: As the Backend2BackendRest service is also reliant on an up-and-running Metadataservice, I guess this check could even serve as a readiness probe, even though the Metadata isn't used actually.

[tsicking]

Hi Phil and Chris, While I am honoured that I have been chosen as a reviewer for this PR, I have to say that I work predominantly on the OpenEMS edge, and not on the backend. All I can say is that

1. "Allow unauthenticated access" seems a bit dangerous to me
2. Two dependencies are added to pom.xml. I am always very careful with changing this file. I can't judge whether the impact of this PR justifies that, but I would be very careful with that.

[sfeilmeier]

@michaelgrill What's your opinion on this?

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[github-actions[bot]]

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