Zammad: Contact form: Change/add categories, questions and links

This issue is basically about updating the contact form so that it includes:

• Subjects NL and EN
• FAQ links NL and EN
• The accompanying "probleem:" headers

• Check and tweak

• When this is done, make sure to store the instructions is a place where we can find it back

See for the full issue: https://code.greenhost.net/greenhost/greenhost/-/issues/639

When this issue is closed, also remember to:

• close the above linked issue