DEV: Add Higher Logic import script (PR #12623)

Wrote up a new script to import from Higher Logic. Nothing too crazy going on here. Two major things about this script:

  1. It requires you to convert a Microsoft SQL file to a format MySQL can read.
  2. Higher Logic stores posts (at least in the case of the import I ran) with the email thread shown in the post body. The script does its best to truncate this out, but the logic may need to be improved on future imports. For the import I ran, it worked just fine as is. :man_shrugging: