## 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
name="cohort_1",
            groups=[{"properties": [{"key": "key", "value": "value", "type": "person"}]}],
        )
        cohort2 = _create_cohort(
            team=self.team,
            name="cohort_2",
            groups=[{"properties": [{"key": "key_2", "value": "value_2", "type": "person"}]}],
        )
        
        cohort1.calculate_people_ch(pending_version=1)
        cohort2.calculate_people_ch(pending_version=0)
        with self.settings(USE_PRECALCULATED_CH_COHORT_PEOPLE=True):  
            with freeze_time("2020-01-04T13:01:01Z"):
                res = self._run(
                    Filter(
                        team=self.team,
                        data={
                            "date_from": "-7d",
                            "events": [{"id": "$pageview"}],
                            "properties": [],
                            "breakdown": [cohort1.pk, cohort2.pk],
                            "breakdown_type": "cohort",
                        },
                    ),
                    self.team,
                )
        self.assertEqual(res[0]["count"], 2)
        self.assertEqual(res[1]["count"], 1)
    @also_test_with_materialized_columns(person_properties=["key", "key_2"], verify_no_jsonextract=False)
    def test_breakdown_single_cohort(self):