## Is your feature request related to a problem?

#4947 added a new query to the backend – time to convert. It works well, just one point is kind of rough: bin width and count.

## Describe the solution you'd like

Currently the number of bins is hardcoded. Ideally we should have two options:
- return a user-specified number of bins,
- otherwise infer a reasonable number of bins using some algorithm (auto option).

@alexkim205 [suggested](https://github.com/PostHog/posthog/issues/4855#issuecomment-872423877) the [Freedman-Diaconis rule](https://en.wikipedia.org/wiki/Freedman%E2%80%93Diaconis_rule) for determining bin width (and interval based on that), but unfortunately from my testing its formula would not be the most practical – it's great for keeping a pretty constant "smoothness" of the histogram esp. with normal distribution, but we face some additional constraints that make it less than ideal:
- we can't have histograms too dense visually in the UI, from my testing a practical limit is 60 bins (above that it gets too dense),
- our data generally doesn't follow much of a normal distribution.

Clamping may help though, or maybe a different formula may work better outright – I'll be testing this.

## Additional context

Issue pertaining to the experience of time to convert: #4855

#### *Thank you* for your feature request – we love each and every one!

posthog/models/filters/mixins/common.py
@cached_property
    def formula(self) -> Optional[str]:
        formula = self._data.get(FORMULA, None)
        if not formula:
            return None
        return "".join(re.findall(ALLOWED_FORMULA_CHARACTERS, formula))
    @include_dict
    def formula_to_dict(self):
        return {"formula": self.formula} if self.formula else {}
class BreakdownMixin(BaseParamMixin):
    def _process_breakdown_param(self, breakdown: Optional[str]) -> Optional[Union[str, List[Union[str, int]]]]:
        if not isinstance(breakdown, str):
            return breakdown
        try:
            return json.loads(breakdown)
        except (TypeError, json.decoder.JSONDecodeError):
            return breakdown
    @cached_property
    def breakdown(self) -> Optional[Union[str, List[Union[str, int]]]]:
        breakdown = self._data.get(BREAKDOWN)
        return self._process_breakdown_param(breakdown)
    @include_dict
    def breakdown_to_dict(self):
        return {"breakdown": self.breakdown} if self.breakdown else {}
class BreakdownTypeMixin(BaseParamMixin):