Ability to auto-enable a default deploy key for new projects

Description

In some situations it's impossible to use the project_created system webhook when you want to clone a repository on another server upon creation.

Because when creating a new project, a default deploy key cannot be automatically enabled for the newly created project. And this results in not beeing able to clone the repository via SSH from another server upon upon creation.

Proposal

Please add an option to deploy keys, either key based for the whole system or in some group setting, so that every newly created project (system wide or group wide) gets this deploy key assinged and enabled automatically.

Links / references

gitlab-ce#20000