Create a test feature for K/V store

We want to create a test feature for K/V store feature.

The feature will be configurable in a similar way than CoreFeature, we will be able to change K/V implementation by using a specific maven profile or specific property.

This feature will get nuxeo.test.kv.implementation property to decide which K/V implementation we need to deploy for unit tests. Fallback will be the in memory implementation.

We should leverage customdb,mongodb for MongoDB implementation choice and nuxeo.test.redis.mode=server property for Redis implementation choice.

In case of conflict, Redis implementation will have precedence over MongoDB one.