## 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.assertEqual([resp["aggregated_value"] for resp in daily_response], [12.5, 10, 1])
        with freeze_time("2020-01-04T13:00:01Z"):
            weekly_response = self._run(
                Filter(
                    team=self.team,
                    data={
                        "display": TRENDS_TABLE,
                        "interval": "day",
                        "breakdown": "$some_property",
                        "events": [
                            {
                                "id": "sign up",
                                "math": "median",
                                "math_property": "$session_duration",
                            }
                        ],
                    },
                ),
                self.team,
            )
        self.assertEqual(
            [resp["breakdown_value"] for resp in daily_response],
            [resp["breakdown_value"] for resp in weekly_response],
        )
        self.assertEqual(
            [resp["aggregated_value"] for resp in daily_response],
            [resp["aggregated_value"] for resp in weekly_response],
        )
    @snapshot_clickhouse_queries
    def test_trends_person_breakdown_with_session_property_single_aggregate_math_and_breakdown(self):