## 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
"""
    When providing an absolutely-formatted URL
    we will not provide one that has an unexpected hostname
    because an attacker might use that to redirect traffic somewhere *bad*
    """
    pass
def absolute_uri(url: Optional[str] = None) -> str:
    """
    Returns an absolutely-formatted URL based on the `SITE_URL` config.
    If the provided URL is already absolutely formatted
    it does not allow anything except the hostname of the SITE_URL config
    """
    if not url:
        return settings.SITE_URL
    provided_url = urlparse(url)
    if provided_url.hostname and provided_url.scheme:
        site_url = urlparse(settings.SITE_URL)
        provided_url = provided_url
        if (
            site_url.hostname != provided_url.hostname
            or site_url.port != provided_url.port
            or site_url.scheme != provided_url.scheme
        ):
            raise PotentialSecurityProblemException(f"It is forbidden to provide an absolute URI using {url}")
    return urljoin(settings.SITE_URL.rstrip("/") + "/", url.lstrip("/"))
def get_previous_day(at: Optional[datetime.datetime] = None) -> Tuple[datetime.datetime, datetime.datetime]: