dev: mockslack UI

[mastercactapus]

Split from #2554

What problem would you like to solve? Please describe: To develop the Slack functionality of GoAlert, you need a Slack workspace and account and publicly-routable access to your development machine.

This is difficult for enterprises wishing to contribute or developers to test/evaluate the project.

Describe the solution you'd like: Add a UI to the mockslack tool that emulates the basic features of Slack necessary for using & testing GoAlert's functionality.

Describe alternatives you've considered: Using tools like ngrok or sendit (in repo) to route traffic during development.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity.