## Bug description

The grouped-by-month view in charts is hella confusing. The x-axis shows a date that does not reflect the value on the y-axis.

1. the y-axis shows the number for the END of the month
2. the x-axis reads as "beginning of the month"

![CleanShot 2024-02-05 at 10 23 30@2x](https://github.com/PostHog/posthog/assets/35429197/d78df745-8319-4b78-95fa-d96f18aee357)

### Comparison with daily grouping

Compare the "group by month" view with "group by day". The x-axis labeling aligns with the y-axis values. 

![CleanShot 2024-02-05 at 10 29 20@2x](https://github.com/PostHog/posthog/assets/35429197/998825fa-7406-4214-8310-8f173980f80c)


## How to reproduce

1. Group a chart by month 
2. select "unique events"

## Proposal 

### 1. easy fix - remove the "1." from the labelling

- will still confuse readers with "is this the beginning or end of the month"

![CleanShot 2024-02-05 at 10 23 30@2x](https://github.com/PostHog/posthog/assets/35429197/1a0ae6d4-0e02-4b32-86ab-7b0e069655ed)

### 2. correct fix - show end of month

- removes ambiguity from "is that the beginning or end of month"
- harder to implement because months have different end days

![CleanShot 2024-02-05 at 10 23 30@2x](https://github.com/PostHog/posthog/assets/35429197/61226346-7f97-4bcd-87bf-53fc83c75245)


cc @jannesblobel
posthog/hogql_queries/insights/trends/test/test_trends.py
ret_dict: Dict[str, Optional[Union[str, int]]] = {}
    if not value or not isinstance(value, str) or "cohort_" not in value:
        label = value if (value or isinstance(value, bool)) and value != "None" and value != "nan" else "Other"
        ret_dict["label"] = f"{entity.name} - {label}"
        ret_dict["breakdown_value"] = label
    else:
        if value == "cohort_all":
            ret_dict["label"] = f"{entity.name} - all users"
            ret_dict["breakdown_value"] = "all"
        else:
            cohort = Cohort.objects.get(pk=value.replace("cohort_", ""))
            ret_dict["label"] = f"{entity.name} - {cohort.name}"
            ret_dict["breakdown_value"] = cohort.pk
    return ret_dict
def _create_action(**kwargs):
    team = kwargs.pop("team")
    name = kwargs.pop("name")
    properties = kwargs.pop("properties", {})
    action = Action.objects.create(team=team, name=name)
    ActionStep.objects.create(action=action, event=name, properties=properties)
    return action
def _create_cohort(**kwargs):
    team = kwargs.pop("team")
    name = kwargs.pop("name")
    groups = kwargs.pop("groups")
    cohort = Cohort.objects.create(team=team, name=name, groups=groups, last_calculation=timezone.now())
    cohort.calculate_people_ch(pending_version=0)
    return cohort
def _props(dict: Dict):