Make slack env variable required

[bbelderbos]

I did not have it set and got this when clicking on an artist:

  File "/Users/bbelderbos/code/pdm/gerardo/commandCenter/centralHub/slackbot/slackbot_api.py", line 15, in post_slack_message
    response = requests.post(SLACk_WEBHOOK, headers=headers, data=json.dumps(data))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/bbelderbos/code/pdm/gerardo/commandCenter/venv/lib/python3.11/site-packages/requests/api.py", line 115, in post
    return request("post", url, data=data, json=json, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/bbelderbos/code/pdm/gerardo/commandCenter/venv/lib/python3.11/site-packages/requests/api.py", line 59, in request
    return session.request(method=method, url=url, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/bbelderbos/code/pdm/gerardo/commandCenter/venv/lib/python3.11/site-packages/requests/sessions.py", line 575, in request
    prep = self.prepare_request(req)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/bbelderbos/code/pdm/gerardo/commandCenter/venv/lib/python3.11/site-packages/requests/sessions.py", line 486, in prepare_request
    p.prepare(
  File "/Users/bbelderbos/code/pdm/gerardo/commandCenter/venv/lib/python3.11/site-packages/requests/models.py", line 368, in prepare
    self.prepare_url(url, params)
  File "/Users/bbelderbos/code/pdm/gerardo/commandCenter/venv/lib/python3.11/site-packages/requests/models.py", line 439, in prepare_url
    raise MissingSchema(
requests.exceptions.MissingSchema: Invalid URL 'None': No scheme supplied. Perhaps you meant https://None?

Because:

SLACk_WEBHOOK = os.getenv("SLACK_C2NOTIFIER")

Defaults to None

Also might want to lower case the k in the variable.

[bbelderbos]

Or don't do the requests.post if the slack webhook is not set.