Add a 'Limit' option for List Fields

[ItsMeAra]

When using The List Field it would be nice to be able to set a limit on the number of Items that can be added through the admin. For example, I tried limit: 1 but didn't do anything, still allows unlimited items.

header.hero_button:
  name: button
  type: list
  label: Button
  limit: 1  # <~ this would be great!
  fields:
    .text:
      type: text
      label: Button Text
      validate:
        required: true
    .url:
      type: text
      label: Button URL
      validate:
        required: true
    .theme:
      type: select
      label: Button Color
      options:
          1: 'Blue'
          0: 'Green'

Discovered in Slack chat that this is not a current feature. Would be nice to add. 😄

[dimitrilongo]

Same here #720

[w00fz]

Fixed in #1113, thanks @david-szabo97