## 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
with freeze_time("2020-01-04T13:00:01Z"):
            response = self._run(
                Filter(
                    team=self.team,
                    data={
                        "display": "ActionsLineGraph",
                        "interval": "day",
                        "events": [{"id": "sign up", "math": "unique_session"}],
                        "breakdown": "$session_duration",
                        "breakdown_type": "session",
                        "insight": "TRENDS",
                        "breakdown_histogram_bin_count": 3,
                        "properties": [{"key": "$some_prop", "value": "some_val", "type": "person"}],
                        "date_from": "-3d",
                    },
                ),
                self.team,
            )
            self.assertEqual(
                [(item["breakdown_value"], item["count"], item["data"]) for item in response],
                [
                    ("[4.95,10.05]", 2.0, [2.0, 0.0, 0.0, 0.0]),
                    ("[0.0,4.95]", 1.0, [1.0, 0.0, 0.0, 0.0]),
                    ("[10.05,15.01]", 1.0, [0.0, 1.0, 0.0, 0.0]),
                    ('["",""]', 0.0, [0.0, 0.0, 0.0, 0.0]),
                ],
            )
    @also_test_with_person_on_events_v2
    @also_test_with_materialized_columns(person_properties=["name"], verify_no_jsonextract=False)
    def test_trends_breakdown_single_aggregate_cohorts(self):