## 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
tq = TrendsQuery(
        series=series,
        kind="TrendsQuery",
        filterTestAccounts=filter.filter_test_accounts,
        dateRange=DateRange(date_from=filter_as_dict.get("date_from"), date_to=filter_as_dict.get("date_to")),
        samplingFactor=filter.sampling_factor,
        aggregation_group_type_index=filter.aggregation_group_type_index,
        breakdownFilter=BreakdownFilter(
            breakdown=filter.breakdown,
            breakdown_type=filter.breakdown_type,
            breakdown_normalize_url=filter.breakdown_normalize_url,
            breakdowns=filter.breakdowns,
            breakdown_group_type_index=filter.breakdown_group_type_index,
            breakdown_histogram_bin_count=filter.breakdown_histogram_bin_count,
        ),
        properties=_props(filter.to_dict()),
        interval=filter.interval,
        trendsFilter=TrendsFilter(
            display=filter.display,
            breakdown_histogram_bin_count=filter.breakdown_histogram_bin_count,
            compare=filter.compare,
            formula=filter.formula,
            smoothingIntervals=filter.smoothing_intervals,
        ),
    )
    return tq
@override_settings(IN_UNIT_TESTING=True)
class TestTrends(ClickhouseTestMixin, APIBaseTest):
    maxDiff = None
    def _run(self, filter: Filter, team: Team):