[IEC][SEBA] Create helm repository for combined release charts

With the new SEBA version we have ported recently, based on CORD Platform 7.0, we have switched to using SEBA-in-a-Box from the very beginning, since it made more sense from a CI perspective.

However, it's still a good idea to create and make available proper helm charts for deploying SEBA using the helm charts only, the same way Opencord releases them on https://charts.opencord.org/

Here we are talking about creating the combined charts for cord-platform, seba and att-workflow and a corresponding helm repository. The last piece we needed to be able to do this was porting a series of images for logging and nem-monitoring, which is covered in IEC-40. With this occasion, two helm repositories were also created using github pages, in https://iecedge.github.io/helm-k8s-charts/stable/index.yaml and https://iecedge.github.io/helm-k8s-charts/incubator/index.yaml, as described in IEC-40.

My proposal for now is to do the same thing for the https://github.com/iecedge/helm-charts, and place the charts there.