Make header take custom fields

[gmegh]

Add the possibility of adding custom fields in the header to store simulation information. For instance, here:

header:
    mjd-obs: $mjd  # Start of observation
    mjd: $mjd+17/86400.0  # Write time of data writing to file
    seqnum: $seqnum
    band: $band
    fieldRA: $boresight.ra.deg
    fieldDec: $boresight.dec.deg
    rotTelPos: $rtp.deg
    airmass: $airmass
    runnum: 1

[jchiang87]

@gmegh As it turns out, this sort of functionality is already available. Here's the syntax for the imsim yaml file:

output.readout.added_keywords: {'RA': $boresight.ra.deg, 'DEC': $boresight.dec.deg,...}

The following should also work:

output.readout.added_keywords:
    RA: $boresight.ra.deg
    DEC: $boresight.dec.deg

You can use whatever keywords you want in that dictionary, but note that if you want to overwrite a standard keyword, e.g., RA, DEC, you need to specify it explicitly.

If this works for you, please close this issue.