Minor Change to slug of the `download-starter-project` endpoint

[michael-valdron]

Which area/kind this issue is related to?

/area registry

Issue Description

for #781

This would change the slug from GET /devfiles/<stack>/starterProjects/<starterProjectName> to GET /devfiles/<stack>/starter-projects/<starterProjectName>, this would as well change the multi version from GET /devfiles/<stack>/<version>/starterProjects/<starterProjectName> to GET /devfiles/<stack>/<version>/starter-projects/<starterProjectName>.

Target Date: 06-09-2022