Add Slack integration

[sibios]

Utilize Slack webhooks for notifications similar to the existing discord notifications. Minor tweak on wording to allow for notifications on door bumps.

Fixes: #280

[jabelone]

Looking great, thanks! Just have a few small changes suggested and it should be good to merge. I haven't physically tested this branch myself, but it looks fine to me once those changes are made.

[jabelone]

Oh also looks like you may need to run black to auto format a couple things :) https://github.com/membermatters/MemberMatters/actions/runs/12531411171/job/35163781642?pr=286

[sibios]

these two additional commits should cover the requested changes. Please let me know if you think anything else should be modified for the PR to be merged. I have left as a TODO (probably need to cut an issue) to generic-ize the "Report via webhook" feature either (1) turning that into a abstract class for specific service classes to implement or (2) providing some sort of minimal templating DSL for admins to provide, have MM render, and then sling at a specified webhook.

[jabelone]

Thanks, merged :)