## 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
continue  
                elif is_boolean_breakdown:
                    label = self._convert_boolean(value)
                else:
                    label = str(value)
                item = BreakdownItem(label=label, value=value)
                if item not in res_breakdown:
                    res_breakdown.append(item)
        return InsightActorsQueryOptionsResponse(
            series=res_series, breakdown=res_breakdown, day=res_days, compare=res_compare
        )
    def calculate(self):
        queries = self.to_query()
        if len(queries) == 1:
            resonse_hogql_query = queries[0]
        else:
            resonse_hogql_query = ast.SelectUnionQuery(select_queries=[])
            for query in queries:
                if isinstance(query, ast.SelectQuery):
                    resonse_hogql_query.select_queries.append(query)
                else:
                    resonse_hogql_query.select_queries.extend(query.select_queries)
        with self.timings.measure("printing_hogql_for_response"):
            response_hogql = to_printed_hogql(resonse_hogql_query, self.team, self.modifiers)
        res_matrix: List[List[Any] | Any | None] = [None] * len(queries)
        timings_matrix: List[List[QueryTiming] | None] = [None] * len(queries)
        errors: List[Exception] = []
        def run(index: int, query: ast.SelectQuery | ast.SelectUnionQuery, is_parallel: bool):