Allow customization of Aeon form defaults

[ctgraham]

Is your feature request related to a problem? Please describe.

Branching from #228, and pending any migration to using the Aeon API directly for requests, the Grouping / Concatenation / FirstValue settings, the Reading Room defaults, and the Duplication defaults are likely candidates for institutional customization.

Describe the solution you'd like

Either configuration variables to localize these settings, or settings editable in the Django application.

Describe alternatives you've considered

The alternate approach of using the Aeon API to directly write to Aeon seems like a subsequent effort to me, following a low-effort implementation of configuring the form-based interaction.

Additional context

n/a

[ctgraham]

We should also note in the configuration that the effective selection of Grouping / Concatenation / FirstValue settings is dependent on the Aeon GroupRequestsByLocation key:
https://support.atlas-sys.com/hc/en-us/articles/360011919533-Submitting-Requests-via-EAD-Finding-Aids

If this key is set to "No", the Grouping* fields are ineffective/irrelevant.