## 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
"breakdown": "name",
                        "breakdown_type": "person",
                        "display": "ActionsPie",
                        "events": [
                            {
                                "id": "watched movie",
                                "name": "watched movie",
                                "type": "events",
                                "order": 0,
                                "math": "dau",
                                "properties": [
                                    {
                                        "key": "name",
                                        "operator": "not_icontains",
                                        "value": "person3",
                                        "type": "person",
                                    }
                                ],
                            }
                        ],
                    }
                ),
                self.team,
            )
            event_response = sorted(event_response, key=lambda resp: resp["breakdown_value"])
            self.assertEqual(len(event_response), 2)
            self.assertDictContainsSubset({"breakdown_value": "person1", "aggregated_value": 1}, event_response[0])
            self.assertDictContainsSubset({"breakdown_value": "person2", "aggregated_value": 1}, event_response[1])
    @also_test_with_materialized_columns(person_properties=["name"])
    def test_filter_test_accounts_cohorts(self):