## 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
"""
    Decodes base64 bytes into string taking into account necessary transformations to match client libraries.
    """
    if not isinstance(data, str):
        data = data.decode()
    data = base64.b64decode(data.replace(" ", "+") + "===")
    return data.decode("utf8", "surrogatepass").encode("utf-16", "surrogatepass")
def decompress(data: Any, compression: str):
    if not data:
        return None
    if compression == "gzip" or compression == "gzip-js":
        if data == b"undefined":
            raise RequestParsingError(
                "data being loaded from the request body for decompression is the literal string 'undefined'"
            )
        try:
            data = gzip.decompress(data)
        except (EOFError, OSError, zlib.error) as error:
            raise RequestParsingError("Failed to decompress data. %s" % (str(error)))
    if compression == "lz64":
        KLUDGES_COUNTER.labels(kludge="lz64_compression").inc()
        if not isinstance(data, str):
            data = data.decode()
        data = data.replace(" ", "+")
        data = lzstring.LZString().decompressFromBase64(data)