Open issues from alerts as `GitLab Alert Bot`

We are currently working on the support for opening issues from alerts: https://gitlab.com/gitlab-org/gitlab-ee/issues/4925#note_146390734

However we need a user to set as the "author" of these issues. We are going to ship the first iteration behind a feature flag, which opens issues with the built-in ghost user a the author, in order to be able to start doing some testing with customers.

Issues opened as a ghost user are not ideal though, and we need our own Bot user that we can use to open these issues under, like Service Desk. (GitLab Support Bot)

Proposal

We should create another bot user called GitLab Alert Bot, and open all new issues from alerts under that user.