Implement Slack App Manifest

[krzysztofwolski]

It seems to we'll be able to make the installation process more user-friendly using Slack App Manifest: https://api.slack.com/reference/manifests#sharing_manifests .

Requirements:

• [ ] Add app manifest with required webhooks
• [ ] Configuration view at Saleor Dashboard should have a button to connect our App to Slack instead of a manual webhook setup

[krzysztofzuraw]

I've dug a bit of Slack documentation and I've found out that you can programmatically receive a webhook URL when the user creates an app (doc reference).

I'm attaching a screenshot as Slack docs can't link to headers 🤷

Proposed flow

sequenceDiagram
    participant app
    participant slack
    app->>slack: share app manifest
    slack->>app: send back webhook URL
    app->>app: saves webhook URL

[krzysztofzuraw]

After further investigation, I found out that implementing the changes proposed by my comment will require migrating to OAuth flow so I will skip this part for now.