Add domain field to Auto DevOps application setting

Description

Auto DevOps includes an application setting that allows instance admins to enable the feature instance wide. In order to have Auto Review App and Auto Deploy working, a domain has to be specified. At the moment, it is possible only at project-level, so enabling Auto DevOps at instance level is not enough to make it fully functional.

Proposal / Design

Add an instance setting that specifies domain at the same way we have it at project-level.

It is an inputbox similar to what we have in CI/CD > Settings (see https://gitlab.com/gitlab-org/gitlab-ce/issues/38175#note_53324166), but with the following text:

Specify a domain to use by default for every project's Auto Review Apps and Auto Deploy stages.

Allow configuring Auto DevOps when using charts: https://gitlab.com/charts/charts.gitlab.io/issues/103

Links / references

Auto DevOps (Beta): #37115 (closed)
Integrate usage of an implicit .gitlab-ci.yml for Auto DevOps: #34777 (closed)

Edited Jan 10, 2018 by Dimitrie Hoekstra