https://linear.app/unleash/issue/2-1232/implement-first-iteration-of-the-new-slack-app-addon
This PR implements the first iteration of the new Slack App addon.
Unlike the old Slack addon, this one uses a Slack App (bot) that is
installed to Slack workspaces in order to post messages. This uses
`@slack/web-api`, which internally uses the latest Slack API endpoints
like `postMessage`.
This is currently behind a flag: `slackAppAddon`.
The current flow is that the Unleash Slack App is installed from
whatever source:
- Unleash addons page;
- Direct link;
- https://unleash-slack-app.vercel.app/ (temporary URL);
- Slack App Directory (in the future);
- Etc;
After installed, we resolve the authorization to an `access_token` that
the user can paste into the Unleash Slack App addon configuration form.
https://github.com/Unleash/unleash/assets/14320932/6a6621b9-5b8a-4921-a279-30668be6d46c
Co-authored by: @daveleek
---------
Co-authored-by: David Leek <david@getunleash.io>
