Add default resolver to Lighthouse docker images.

[ghost]

Using the recently added environment variable configuration via akkadotnet-bootstrap, I've added the default configuration as follows:

akka.cluster.split-brain-resolver.active-strategy=keep-majority

Closes #115

[claassistantio]

All committers have signed the CLA.

[ghost]

This was done because ENV values are not transferrable between intermediate containers. And, we need the config visible to the final runtime image
.

[Aaronontheweb]

LGTM