## 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
delta_mapping["weeks"] = int(match.group("number"))
    elif match.group("type") == "m":
        if match.group("number"):
            delta_mapping["months"] = int(match.group("number"))
        if match.group("position") == "Start":
            delta_mapping["day"] = 1
        elif match.group("position") == "End":
            delta_mapping["day"] = 31
    elif match.group("type") == "q":
        if match.group("number"):
            delta_mapping["weeks"] = 13 * int(match.group("number"))
    elif match.group("type") == "y":
        if match.group("number"):
            delta_mapping["years"] = int(match.group("number"))
        if match.group("position") == "Start":
            delta_mapping["month"] = 1
            delta_mapping["day"] = 1
        elif match.group("position") == "End":
            delta_mapping["month"] = 12
            delta_mapping["day"] = 31
    parsed_dt -= relativedelta(**delta_mapping)  
    if always_truncate:
        
        
        if "hours" in delta_mapping:
            parsed_dt = parsed_dt.replace(minute=0, second=0, microsecond=0)
        else:
            parsed_dt = parsed_dt.replace(hour=0, minute=0, second=0, microsecond=0)
    return parsed_dt, delta_mapping, match.group("position") or None
def relative_date_parse(