## 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
res_breakdown: List[BreakdownItem] | None = None
        res_series: List[Series] = []
        res_compare: List[CompareItem] | None = None
        
        res_days: List[DayItem] = [DayItem(label=day, value=day) for day in self.query_date_range.all_values()]
        
        for index, series in enumerate(self.query.series):
            series_label = self.series_event(series)
            res_series.append(Series(label="All events" if series_label is None else series_label, value=index))
        
        if self.query.trendsFilter is not None and self.query.trendsFilter.compare:
            res_compare = [
                CompareItem(label="Current", value="current"),
                CompareItem(label="Previous", value="previous"),
            ]
        
        for series in self.query.series:
            
            
            query_date_range = self.query_date_range
            query_builder = TrendsQueryBuilder(