Sentry Issue: [POSTHOG-EU-3K](https://sentry.io/organizations/posthog/issues/3662211615/?referrer=github_integration)

```
ValidationError: {'events': [{'math': [ErrorDetail(string='"avg" is not a valid choice.', code='invalid_choice')]}]}
  File "posthog/api/insight.py", line 604, in trend
    serializer.is_valid(raise_exception=True)
  File "rest_framework/serializers.py", line 228, in is_valid
    raise ValidationError(self.errors)
```
posthog/models/entity/entity.py
"p90",
    "p95",
    "p99",
    "min_count_per_actor",
    "max_count_per_actor",
    "median_count_per_actor",
    "p90_count_per_actor",
    "p95_count_per_actor",
    "p99_count_per_actor",
]
class Entity(PropertyMixin):
    """
    Entities represent either Action or Event objects, nested in Filter objects.
    This object isn't a table in the database. It gets stored against the specific models itself as JSON.
    This class just allows for stronger typing of this object.
    """
    id: Union[int, str]
    type: Literal["events", "actions"]
    order: Optional[int]
    name: Optional[str]
    custom_name: Optional[str]
    math: Optional[MathType]
    math_property: Optional[str]
    math_group_type_index: Optional[GroupTypeIndex]
    
    
    
    
    index: int
    def __init__(self, data: Dict[str, Any]) -> None: