Select applications to install in the Cluster creation form

Problem to solve

Users are unable to specify which applications they would like installed on their clusters on the cluster creation form. They have to wait until after the cluster is created to specify this.

Additionally, once the cluster is created, users have to first install tiller before they can specify any further applications they'd like to install.

Further details

As a user, I may know which applications are to be installed on this cluster or trust gitlab to provide me with the necessary applications for I'm looking to accomplish.

Proposal

Through a wizard, provide the ability to define which application(s) are to be installed on the cluster after it is created on the cluster creation form. After the cluster is created then install the applications specified by the user.

If the user selects to install any given application without prior having checked tiller, tiller is then automatically checked (with a blurb maybe?)

Just like we have in the current app installation area, a brief explanation of what the apps does.

Links / references

Matching design issue https://gitlab.com/gitlab-org/gitlab-ce/issues/42072

/label ~"feature proposal"