Add support for modals / forms

[merlinfuchs]

Original message: https://discord.com/channels/730045476459642900/1235870818777698355

• New “Forms” section on the dashboard
• Customize these fields for each question:
  • Label
  • Placeholder
  • Singleline or multiline
  • Preset character (If a text is already written in the field, by default)
  • Required or not
  • Minimum and maximum characters (I believe the maximum number of characters per Discord is between 4000 and 5000)
  • Choose form title
• When creating a message in the editor, associate a form with a button or selector (or command if premium).
• Create and personalize a message with variables that indicate what the user has written in the form.