title: Django JSONField Constraint
body: <p>I have a model that represents an email, which was sent via my Provider X.
  Im getting a callback from X with data, that I would like to save in the field called <code>additional_recipients</code>. Because of some mailing list only allowing 5 max additional recipients, i need to limit the jsonfield to only contain max 5 emails per row</p>
  <pre class="lang-py prettyprint-override"><code>class EmailCallback(models.Model):
      additional_recipients = models.JSONField(default=list)
  </code></pre>
  <p>Is it possible, to limit the JsonField so it it only holds max 5 values?</p>
  <pre><code> [{&quot;value&quot;: &quot;email1&quot;}, {&quot;value&quot;: &quot;email2&quot;}, {&quot;value&quot;: &quot;email3&quot;}, {&quot;value&quot;: &quot;email4&quot;}]
  </code></pre>
  <p>I know i can do</p>
  <pre><code>    class Meta:
          constraints = [
              CheckConstraint(...)
          ]
  </code></pre>
  <p>But i was wondering if thats even doable? Using Django 3.2.8 :)</p>