Add new non scalar: `taken_by`

• See log file: github-action-thunderbird-aaq/actions/runs/23156524910/job/67272681217 which is from question 1571147
• Add a taken_by column to the CSV output of to https://github.com/thunderbird/github-action-thunderbird-aaq/blob/main/get-tb-creator-answers-questions-for-arbitrary-time-period.rb
• Add taken_by to known_non_scalars
• ruby code: q['taken_by'] = q['taken_by']['username'] unless q['taken_by'].nil? # Case is significant.
• in the following example from the log file, the taken_by value is Mapenzi

E, [2026-03-16T17:16:51.724381 #2269] ERROR -- : unknown non scalar: key:taken_by value:{
        "username" => "Mapenzi",
    "display_name" => "Mapenzi",
          "avatar" => "https://firefoxusercontent.com/cf1dc1320d8b99b945b166bd83018b0b"
}

• update the script to make the default values for taken_by, solved_by, and updated_by to be ''