## 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
self.team.timezone = "US/Pacific"
        self.team.save()
        self._create_event_count_per_actor_events()
        with freeze_time("2020-01-03 19:06:34"):
            self._create_person(team_id=self.team.pk, distinct_ids=["another_user"])
            self._create_event(
                team=self.team,
                event="viewed video",
                distinct_id="another_user",
                properties={"color": "orange"},
            )
        daily_response = self._run(
            Filter(
                team=self.team,
                data={
                    "display": TRENDS_LINEAR,
                    "events": [{"id": "viewed video", "math": "dau"}],
                    "breakdown": "color",
                    "date_from": "2020-01-01",
                    "date_to": "2020-03-07",
                    "interval": "month",
                },
            ),
            self.team,
        )
        
        assert daily_response[0]["days"] == ["2020-01-01", "2020-02-01", "2020-03-01"]
        assert daily_response[1]["days"] == ["2020-01-01", "2020-02-01", "2020-03-01"]
        assert daily_response[2]["days"] == ["2020-01-01", "2020-02-01", "2020-03-01"]
    def _create_groups(self):