Slack integration deployment "Started" notification

Problem to solve

The slack integration now notifies when a deployment finishes. Amazing, a much needed feature. Out of complete shortsightedness, it does not notify when a deployment starts (!?!?!).

Many users will want to be notified not only when the deployment finishes, but also when it begins.

Intended users

Everyone

Proposal

In the slack integration, make the "deployment" option "deployment finishes" and then add a "deployment starts" option.