## 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
flush_persons_and_events()
        
        trend_query = convert_filter_to_trends_query(filter)
        tqr = TrendsQueryRunner(team=team, query=trend_query)
        return tqr.calculate().results
    def _get_trend_people(self, filter: Filter, entity: Entity):
        data = filter.to_dict()
        
        if data.get("events", None):
            data["events"] = json.dumps(data["events"])
        if data.get("properties", None):
            data["properties"] = json.dumps(data["properties"])
        with self.settings(DEBUG=True):
            response = self.client.get(
                f"/api/projects/{self.team.id}/persons/trends/",
                data={**data, ENTITY_TYPE: entity.type, ENTITY_ID: entity.id},
                content_type="application/json",
            ).json()
        return response["results"][0]["people"]
    def _create_event(self, **kwargs):