## 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
from posthog.hogql_queries.utils.query_previous_period_date_range import (
    QueryPreviousPeriodDateRange,
)
from posthog.models import Team
from posthog.models.action.action import Action
from posthog.models.cohort.cohort import Cohort
from posthog.models.filters.mixins.utils import cached_property
from posthog.models.property_definition import PropertyDefinition
from posthog.schema import (
    ActionsNode,
    BreakdownItem,
    ChartDisplayType,
    Compare,
    CompareItem,
    DayItem,
    EventsNode,
    HogQLQueryResponse,
    InCohortVia,
    InsightActorsQueryOptionsResponse,
    QueryTiming,
    Series,
    TrendsQuery,
    TrendsQueryResponse,
    HogQLQueryModifiers,
)
class TrendsQueryRunner(QueryRunner):
    query: TrendsQuery
    query_type = TrendsQuery
    series: List[SeriesWithExtras]
    def __init__(