[kept for history for now] Move to plain SLF4J

[rmannibucau]

Overall idea is to move to a real logger implementation, there are multiple pitfalls with current manual buffering/filewriter:

• it is not very customizable (structured logging is hard to do for example)
• it requires to use /dev/null as workaround when in a docker container and enable stdout/stderr
• it is not extensible with common appenders easily even with slf4j listener - kafka my friend to cite it ;)
• it is not easy to auto-instrument (opentelemetry-javaagent or k8s integrations for ex, slf4j is built-in, not custom integrations)
• there is no real notion of MDC or future work on observability

edit: issue ref: #8321

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[bamaer]

Please create tickets for your PRs so we can keep a trace of changes. The initial review showed some significant issues, I can post the full review tomorrow.
More importantly, imho major changes like these should be discussed in a feature request ticket or a discussion first. A PR is not the right place to have this discussion.