Draft: Fix volume mounts not being added for init containers

In https://gitlab.com/gitlab-org/remote-development/devfile-gem/-/merge_requests/11+ , we tried to use the devfile library directly to generate volumes and volume mounts for containers and init containers. From the volumes which were persistent, we generated the PVCs.

As part of the above, we removed the ext/volume.go file since that code was now available in the devfile library.

However, there is probably a bug in the library function which does not update the volume mounts of the init containers. Check https://gitlab.com/gitlab-org/remote-development/devfile-gem/-/merge_requests/15+

This MR is sort of reverting the changes of https://gitlab.com/gitlab-org/remote-development/devfile-gem/-/merge_requests/11+ while making sure the volume mounts are added in both containers and init containers and pvcs are generated for persistent volumes.