## Is your feature request related to a problem?

When sending incorrectly formatted payloads (e.g. a text-based string with a `gzip` compression header), the app will fail with a cryptic 500 error and register an unhandled exception.

## Describe the solution you'd like
The app should return a 400 bad request error, with details on why the request failed (i.e. it is incorrectly formatted or the content does not match the compression specified). In addition, this shouldn't be treated as an unhandled exception as it's a client error.


## Describe alternatives you've considered
Keep returning a cryptic 500 error.


## Additional context
Relevant context on #2701


#### *Thank you* for your feature request – we love each and every one!

posthog/utils.py
"""Return a number in a compact format, with a SI suffix if applicable.
    Client-side equivalent: utils.tsx#compactNumber.
    """
    value = float("{:.3g}".format(value))
    magnitude = 0
    while abs(value) >= 1000:
        magnitude += 1
        value /= 1000.0
    return "{:f}".format(value).rstrip("0").rstrip(".") + ["", "K", "M", "B", "T", "P", "E", "Z", "Y"][magnitude]
def is_postgres_alive() -> bool:
    from posthog.models import User
    try:
        User.objects.count()
        return True
    except DatabaseError:
        return False
def is_redis_alive() -> bool:
    try:
        get_redis_info()
        return True
    except BaseException:
        return False
def is_celery_alive() -> bool:
    try:
        return get_celery_heartbeat() != "offline"
    except BaseException:
        return False
def is_plugin_server_alive() -> bool: