Run all asset compile tasks separately

The run time for the rake gitlab:assets:compile tasks exceeded the default timeout of 2 hours when building on the Scaleway PaaS. Because of the extended period of time needed to complete full execution, we have split the task into the component parts in the recipe for gitlab-rails, so that we are not SIGTERMd to failure at the point of 2 hours. We could have extended the timeout for this task, but felt it more responsible to keep tabs on the performance of the sub-tasks and work with the appropriate teams to reduce these points individually.

Build log: https://dev.gitlab.org/gitlab/omnibus-gitlab/-/jobs/1272407

cc @marin

Closes #2510 (closed)

This can be merged to master, but should likely be pulled to all stable branches.