## 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
try:
                series_with_extra = self.series[index]
                response = execute_hogql_query(
                    query_type="TrendsQuery",
                    query=query,
                    team=self.team,
                    timings=self.timings,
                    modifiers=self.modifiers,
                )
                timings_matrix[index] = response.timings
                res_matrix[index] = self.build_series_response(response, series_with_extra, len(queries))
            except Exception as e:
                errors.append(e)
            finally:
                if is_parallel:
                    from django.db import connection
                    
                    connection.close()
        
        
        if settings.IN_UNIT_TESTING:
            for index, query in enumerate(queries):
                run(index, query, False)
        elif len(queries) == 1:
            run(0, queries[0], False)
        else:
            jobs = [threading.Thread(target=run, args=(index, query, True)) for index, query in enumerate(queries)]