## 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/utils.py
start_date: Optional[datetime.datetime],
    end_date: Optional[datetime.datetime],
    frequency: str,
) -> List[Any]:
    """
    Returns list of a fixed frequency Datetime objects between given bounds.
    Parameters:
        start_date: Left bound for generating dates.
        end_date: Right bound for generating dates.
        frequency: Possible options => minute, hour, day, week, month
    """
    delta = DATERANGE_MAP[frequency]
    if not start_date or not end_date:
        return []
    time_range = []
    if frequency != "minute" and frequency != "hour":
        start_date = start_date.replace(hour=0, minute=0, second=0, microsecond=0)
        end_date = end_date.replace(hour=0, minute=0, second=0, microsecond=0)
    if frequency == "week":
        start_date -= datetime.timedelta(days=(start_date.weekday() + 1) % 7)
    if frequency != "month":
        while start_date <= end_date:
            time_range.append(start_date)
            start_date += delta
    else:
        if start_date.day != 1: