## Is your feature request related to a problem?

Can't define desired message format in an Action.

## Describe the solution you'd like

Increase character limit significantly.

## Describe alternatives you've considered

none

## Additional context

200 characters are way too little, especially if you have lots of variables with long names.
A single placeholder can easily take 50 characters, esp. with the overly long `[event.properties.…]` syntax.

<img width="427" alt="image" src="https://user-images.githubusercontent.com/85242/163712432-7e153e72-4385-453d-9184-287238862a8b.png">


posthog/models/action/__init__.py
return self.name
    def get_analytics_metadata(self):
        return {
            "post_to_slack": self.post_to_slack,
            "name_length": len(self.name),
            "custom_slack_message_format": self.slack_message_format != "",
            "event_count_precalc": self.events.count(),  
            "step_count": self.steps.count(),
            "match_text_count": self.steps.exclude(Q(text="") | Q(text__isnull=True)).count(),
            "match_href_count": self.steps.exclude(Q(href="") | Q(href__isnull=True)).count(),
            "match_selector_count": self.steps.exclude(Q(selector="") | Q(selector__isnull=True)).count(),
            "match_url_count": self.steps.exclude(Q(url="") | Q(url__isnull=True)).count(),
            "has_properties": self.steps.exclude(properties=[]).exists(),
            "deleted": self.deleted,
        }
@receiver(post_save, sender=Action)
def action_saved(sender, instance: Action, created, **kwargs):
    get_client().publish("reload-action", json.dumps({"teamId": instance.team_id, "actionId": instance.id}))
@receiver(post_delete, sender=Action)
def action_deleted(sender, instance: Action, **kwargs):
    get_client().publish("drop-action", json.dumps({"teamId": instance.team_id, "actionId": instance.id}))