## 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
timestamp="2020-01-05T12:00:00Z",
            properties={"fake_prop": "value_1"},
        )
        with freeze_time("2020-01-04T13:01:01Z"):
            data = {
                "date_from": "-14d",
                "breakdown": "fake_prop",
                "breakdown_type": "event",
                "display": "ActionsPie",
                "events": [
                    {
                        "id": "watched movie",
                        "name": "watched movie",
                        "type": "events",
                        "order": 0,
                        "math": "dau",
                    }
                ],
            }
            event_response = self._run(Filter(team=self.team, data=data), self.team)
            event_response = sorted(event_response, key=lambda resp: resp["breakdown_value"])
            entity = Entity({"id": "watched movie", "type": "events", "math": "dau"})
            people_value_1 = self._get_trend_people(
                Filter(team=self.team, data={**data, "breakdown_value": "value_1"}),
                entity,
            )
            assert people_value_1 == [
                
                {
                    "created_at": "2020-01-01T12:00:00Z",