[draft] bfabric-app-runner docs

[leoschwarz]

there were some earlier efforst in #220 which should be merged into this branch as well

[github-actions]

📝 "TODO" Changes Detected

Summary: ➕ 1 "TODO" added

➕ Added "TODO"s (1)

• bfabric_app_runner/docs/api_reference/specs/output_specification.md:49: - The workunit ID needs to be specified, so the correct information can be retrieved. (TODO but instead of the workunit id it should also be possible to pass the ref)

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This comment is automatically updated when "TODO" changes are detected.