AOD: Possibility to inject additional meta data

[sawenzel]

AOD: Possibility to inject additional meta data

Commit provides possibility to inject additional (non-hard-coded)
meta data into AOD. This could be used by MC to add information about
timeframe length used or other specific configurations etc.

The commit relates to https://its.cern.ch/jira/browse/O2-6027

By default this does not change any production behaviour. Existing
meta data is not touched.

This works by generating a simple key-value json (foo.json) like

{
    "ALIEN_JDL_MC_ORBITS_PER_TF": "4",
    "ALIEN_JDL_ANCHOR_SIM_OPTIONS": "-gen pythia8"
}

and then exporting an environment variable pointing to this json.

export AOD_ADDITIONAL_METADATA_FILE=${PWD}/foo.json

[github-actions]

REQUEST FOR PRODUCTION RELEASES:
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The following labels are available
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[alibuild]

Error while checking build/O2/fullCI_slc9 for 0c0ea9a at 2025-06-04 19:42:

## sw/BUILD/O2-latest/log
/sw/SOURCES/O2/14362-slc9_x86-64/0/Detectors/AOD/src/AODProducerWorkflowSpec.cxx:106:10: fatal error: nlohmann/json.hpp: No such file or directory
ninja: build stopped: subcommand failed.

Full log here.