Store simtel metaparams in output HDF5 file

[maxnoe]

We should:

• Add a generic way to include simulation configuration key/value pairs to DataWriter, not just the pre-configured run header container object
• Include the simtel metaparams for simtel files

Some points:

• This probably needs to happen by obs-id
• Simtel metaparams are always string keys and string values, although values can semantically be anything (e.g. RANDOM_MONO_PROB is a float)
• tables at the moment does not support variable length string tables, which will create some issues for this

[kosack]

Could we just add a way to dynamically add columns to the SimulationConfiguration? I guess that might break merging though if the number of columns is really different per observation, though we could just do an outer join in the merger.

It would be quiet easy to add a function like:

Container.add_dynamic_column(name:str, field:Field)`