## 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/trends_query_runner.py
self,
        time_frame: Optional[str | int],
        series_index: int,
        breakdown_value: Optional[str | int] = None,
        compare: Optional[Compare] = None,
    ) -> ast.SelectQuery | ast.SelectUnionQuery:
        with self.timings.measure("trends_to_actors_query"):
            series = self.query.series[series_index]
            if compare == Compare.previous:
                query_date_range = self.query_previous_date_range
                delta_mappings = self.query_previous_date_range.date_from_delta_mappings()
                if delta_mappings is not None and time_frame is not None and isinstance(time_frame, str):
                    relative_delta = relativedelta(**delta_mappings)  
                    parsed_dt = parser.isoparse(time_frame)
                    parse_dt_with_relative_delta = parsed_dt - relative_delta
                    time_frame = parse_dt_with_relative_delta.strftime("%Y-%m-%d")
            else:
                query_date_range = self.query_date_range
            query_builder = TrendsQueryBuilder(
                trends_query=self.query,
                team=self.team,
                query_date_range=query_date_range,
                series=series,
                timings=self.timings,
                modifiers=self.modifiers,
            )
            query = query_builder.build_actors_query(time_frame=time_frame, breakdown_filter=breakdown_value)
        return query
    def to_actors_query_options(self) -> InsightActorsQueryOptionsResponse: