Allow full replicaset support for mongodb chart

[groundhog2k]

Extend mongodb chart to allow building a mongodb replication set with arbiter etc.

[PFVriens]

I moved to using more and more of your helm-charts to use on my Mac M1. Was using bitnami before but they don't provide arm64 support currently.

What would it take to get this feature implemented? Happy to test.

[groundhog2k]

In first place, it would take time for analysis what is necessary and studying how it was implemented in the deprecated Kubernetes helm charts repo (https://github.com/helm/charts/tree/master/stable/mongodb-replicaset and https://github.com/helm/charts/tree/master/stable/mongodb).
I did the same for RabbitMQ and Redis to allow a full HA cluster configuration and it took a few days at the end.
My daily job is exhausting at the moment, but I understand the need for it and will start working on it when I have a bit more time.

[groundhog2k]

@PFVriens : I started working on it. It's not that easy because of a few limitations in the default mongodb docker image.