Follow-up from "Interruptible builds for redundant pipelines" about giving user feedback

Problem

The discussion from gitlab-ce!23464 should be addressed about:

When canceling a pipeline if a build has the interruptible: false set` do we need to additionally inform the user?

Proposal

Displaying a message to the user when canceling a pipeline if a build has the interruptible: false set` to a new Issue if that's OK?