## 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
person = self._create_person(
            team_id=self.team.pk,
            distinct_ids=["blabla", "anonymous_id"],
            properties={"$some_prop": "some_val"},
        )
        _, _, secondTeam = Organization.objects.bootstrap(None, team_fields={"api_token": "token456"})
        freeze_without_time = ["2019-12-24", "2020-01-01", "2020-01-02"]
        freeze_with_time = [
            "2019-12-24 03:45:34",
            "2020-01-01 00:06:34",
            "2020-01-02 16:34:34",
        ]
        freeze_args = freeze_without_time
        if use_time:
            freeze_args = freeze_with_time
        with freeze_time(freeze_args[0]):
            self._create_event(
                team=self.team,
                event="sign up",
                distinct_id="blabla",
                properties={"$some_property": "value", "$bool_prop": True},
            )
        with freeze_time(freeze_args[1]):
            self._create_event(
                team=self.team,
                event="sign up",
                distinct_id="blabla",
                properties={"$some_property": "value", "$bool_prop": False},
            )