Configure Couchbase ourselves rather than importing Spring Data's abstract config

[snicoll]

When we integrate with a Spring Data store, we configure things ourselves but we don't do that at the moment for Couchbase. This leads to a rather complex arrangement with a CouchbaseConfigurer interface we have to implement based on what was auto-configured.

For consistency, we should rather configure things ourselves.

[snicoll]

Couchbase V3 is going to be a breaking change so we have an opportunity to harmonize things here. Removing CouchbaseConfigurer means users can no longer expose that interface to tell Spring Boot what components need to be used to create the CouchbaseTemplate. The good news is that V3 rationalizes that to a single component so it's easier to create your own.