Demonstrate usage of lagomExternalProject

[ignasi35]

It's be good if we could show off the usage of lagomExternalJavadslProject in online-auction. It's a rather unknown feature we could demonstrate further to complement the docs

[lakhina]

I am not sure how we bot both lagomExternalJavadslProject way and single build way in same project and still not confuse people

[ignasi35]

The solution to handle multi-repo with Lagom is not demo-ed so it'd be good if we found a way. Maybe having two folders in the root of this repo where one folder contains one (external) service and the other contains all the rest (item, bid, user, transaction, security, webGateway, search, ...).
The isolated service should be dependable since it would often be unavailable, but just like elastcisearch.

We would then change the instructions a bit and be ready.

[TimMoore]

I think that if we want to do this without making it really complicated to use, we would need to deploy the external project to Maven or some other public artifact repository.

[lakhina]

@TimMoore yes, lagom docs says the same