Fix --conf documentation

[Patrick Collins]

Describe the bug
Documentation states that --conf specifies "A path to the configuration file (by default, flowerconfig.py)"

To Reproduce
Attempting to provide a path always fails. (--conf=relative_path/flowerconfig.py -> The module relative_path/flowerconfig was not found., --conf=/absolute_path/flowerconfig.py -> The module /absolute_path/flowerconfig was not found., etc.)

Expected behavior
Documentation should state that it's a python-import-style module. --conf=relative_path.flowerconfig works.

System information
Using flower 1.0.0, celery 4.4.7, and python 3.6.9. (unfortunately)

It was very hard to research this bug/behavior; the main information I could find was in the incorrect documentation. Hopefully this fix can be pushed to docs soon to avoid another person wasting hours figuring this out. Thank you!

[Abyss Watcher]

Hello, for those who also wasted time figuring out how to use custom broker url and ssl files :

celery --config relativepath.celeryconfig flower

With celeryconfig.py based on https://docs.celeryq.dev/en/latest/userguide/configuration.html

My example :

import ssl 

broker_use_ssl =  {
        'keyfile': 'key.pem',
        'certfile': 'certificate.pem',
        'ca_certs': 'ca_certificate.pem',
        'cert_reqs': ssl.CERT_REQUIRED
    }

broker_url='your_url'

[mher]

Fixed in the latest version