Slack notifications for new podcasts

[kookster]

from Paloma:

Hey team, when a podcast is created/imported using Publish, we get a notification in the #support-data-monitoring channel. Can we get the same when a show is setup/imported in feeder?

[cavis]

Okay, here are some requirements:

• Add a controller concern/tooling for sending messages to slack (via the SNS relay). See Exchange for prior art.
• In the app/controllers/podcasts_controller.rb ... after successfully creating a podcast, send a message to #support-data-monitoring
• Bonus points: make it look nice. Include a link back to feeder.

I'm not sure we'll want/need to alert when PodcastImports are created? So let's hold off on that for now, and just do this podcast-created alert.