## 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
new_date_from = new_date_from.replace(hour=0, minute=0, second=0, microsecond=0)
        
        if (
            interval == "day"
            and date_from_delta_mapping
            and date_from_delta_mapping.get("days", None)
            and date_from_delta_mapping["days"] % 7 == 0
            and not date_to_delta_mapping
            and not ignore_date_from_alignment
        ):
            
            
            
            
            
            
            
            
            new_date_from += datetime.timedelta(days=1)
        new_date_to = (new_date_from + diff).replace(hour=23, minute=59, second=59, microsecond=999999)
    return new_date_from, new_date_to
def generate_cache_key(stringified: str) -> str:
    return "cache_" + hashlib.md5(stringified.encode("utf-8")).hexdigest()
def get_celery_heartbeat() -> Union[str, int]:
    last_heartbeat = get_client().get("POSTHOG_HEARTBEAT")
    worker_heartbeat = int(time.time()) - int(last_heartbeat) if last_heartbeat else -1
    if 0 <= worker_heartbeat < 300:
        return worker_heartbeat
    return "offline"
def base64_decode(data):