Fix Spring Data custom repository fragment lookup.

[christophstrobl]

This commit introduces a Substitution for the Spring Data CustomRepositoryImplementationDetector to directly use the CandidateComponentsIndex for repository fragment lookups and adds the missing type hint for the RepositoryFragment required to create the target repository.

This enables fragments following the pattern FragmentInterfaceName | FragmentInterfaceNameImpl to be discovered and registered correctly when annotated with @Component as outlined below.

interface CustomRepository {
	// ... 
}

@Component
class CustomRepositoryImpl implements CustomRepository {
	// ... 
}

interface DomainTypeRepository extends CrudRepository<DomainType, String>, CustomRepository {
	// ... 
}

It also updates the data-elasticsearch example to cover the custom repository setup and retains functionality of the heritage configuration format (used in the data-mongodb).

On the long run it would be beneficial to revisit the ClassPathScanningCandidateComponentProvider for bean lookups using the spring.components index so it supports the in this PR substituted lookup.

---

Closes: #639

[sdeleuze]

@aclement Could you please give us your advice on that question raised by @christophstrobl ?

[aclement]

I think that is worth an issue in its own right. I saw a similar thing whilst working with Josh Long - he was trying to use ClassPathScanningCandidateComponentProvider (IIRC) and it wasn't always able to use the components index - as if the combination of filters you set on it can cause it to not allow index usage.

[sdeleuze]

@christophstrobl Could you please create the issue suggested by Andy?

@aclement Do you think we should merge this PR as it is of should we wait the issue mention above to be fixed?

[aclement]

@sdeleuze I would say this improves things, let's integrate it. We have the issue for improving things further.