## 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
if not timestamp:
        timestamp = timezone.now()
    
    if isinstance(timestamp, str):
        timestamp = parser.isoparse(timestamp)
    else:
        timestamp = timestamp.astimezone(ZoneInfo("UTC"))
    return timestamp.strftime("%Y-%m-%d %H:%M:%S.%f")
def get_crontab(schedule: Optional[str]) -> Optional[crontab]:
    if schedule is None or schedule == "":
        return None
    try:
        minute, hour, day_of_month, month_of_year, day_of_week = schedule.strip().split(" ")
        return crontab(
            minute=minute,
            hour=hour,
            day_of_month=day_of_month,
            month_of_year=month_of_year,
            day_of_week=day_of_week,
        )
    except Exception as err:
        capture_exception(err)
        return None
def generate_short_id():