## 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
for _ in range(10):
        yield 0.1  
    for _ in range(5):
        yield 0.2  
    for _ in range(5):
        yield 0.4  
    for _ in range(5):
        yield 0.8  
    for _ in range(10):
        yield 1.5  
    while True:
        yield 3.0
@async_to_sync
async def wait_for_parallel_celery_group(task: Any, expires: Optional[datetime.datetime] = None) -> Any:
    """
    Wait for a group of celery tasks to finish, but don't wait longer than max_timeout.
    For parallel tasks, this is the only way to await the entire group.
    """
    default_expires = datetime.timedelta(minutes=5)
    if not expires:
        expires = datetime.datetime.now(tz=datetime.timezone.utc) + default_expires
    sleep_generator = sleep_time_generator()
    while not task.ready():
        if datetime.datetime.now(tz=datetime.timezone.utc) > expires:
            child_states = []
            child: AsyncResult
            children = task.children or []
            for child in children: