New GitLab Slack app's deploy notification is formatted incorrectly

Summary

Using the new GitLab Slack app, when receiving deployment notifications, it is being sent as regular markdown rather than Slack's version of markdown, hence leading to a busy notification filled with markdown rather than being nicely formatted. It also takes up a LOT of vertical real estate.

Steps to reproduce

1. Set up the GitLab App for Slack Integration
2. Turn on Deploy notifications
3. Provide a channel where you want to receive said notification

What is the current bug behavior?

You receive a notification that is like this:

Deploy to stage succeeded
[company / category / application](https://gitlab.com/repo/path) with job [#123456789](https://gitlab.com/company/category/app/-/jobs/1234567) by [Name(user.name)](https://gitlab.com/user.name)
[a0e9f32f](https://gitlab.com/commit-urk): Merge branch 'fix-webpack-config' into 'master'

What is the expected correct behavior?

I would expect a notification that is formatted like this:

Deploy to stage succeeded
<https://gitlab.com/company/category/application|company / category / application> with job <https://gitlab.com/job-url|#1234556789> by <https://gitlab.com/user.name|Name (user.name)>
<https://gitlab.com/commit-url|a0e9f32f>: Merge branch 'fix-webpack-config' into 'master'

which would look like this in Slack:

Deploy to stage succeeded company / category / application with job #123456789 by Name (user.name) a0e9f32f: Merge branch 'fix-webpack-config' into 'master'

Output of checks

This bug happens on GitLab.com

Possible fixes