## 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
pass
    else:
        if parsed_dt.tzinfo is None:
            parsed_dt = parsed_dt.replace(tzinfo=timezone_info)
        else:
            parsed_dt = parsed_dt.astimezone(timezone_info)
        return parsed_dt, None, None
    regex = r"\-?(?P<number>[0-9]+)?(?P<type>[a-z])(?P<position>Start|End)?"
    match = re.search(regex, input)
    parsed_dt = (now or dt.datetime.now()).astimezone(timezone_info)
    delta_mapping: Dict[str, int] = {}
    if not match:
        return parsed_dt, delta_mapping, None
    if match.group("type") == "h":
        delta_mapping["hours"] = int(match.group("number"))
    elif match.group("type") == "d":
        if match.group("number"):
            delta_mapping["days"] = int(match.group("number"))
        if match.group("position") == "Start":
            delta_mapping["hour"] = 0
            delta_mapping["minute"] = 0
            delta_mapping["second"] = 0
            delta_mapping["microsecond"] = 0
        elif match.group("position") == "End":
            delta_mapping["hour"] = 23
            delta_mapping["minute"] = 59
            delta_mapping["second"] = 59
            delta_mapping["microsecond"] = 999999
    elif match.group("type") == "w":
        if match.group("number"):