In preparation so that we can create both cluster attached to project
and cluster attached to group.
- Move ClustersController to top level
- Move Clusters::ApplicationsController to top-level too
- Creates a Clusters::BaseController to share common functions
- Do not rely on @project ivar. Anything could set the ivar.
- Fix Vue page components due to new data-page value
Because of the controller change we have gone from
`projects:clusters:new` to `clusters:new`, so we need to update the file
location of the page components. There is somewhere a function that will
convert data-page to a file location.
On that note, projects/clusters/gcp/new/, translate to
Projects::Clusters::Gcp#new doesn't exist so replace that with
clusters/create_gcp/ and clusters/create_user/
