chore: Remove entities service dependency from relationship service [DHIS2-18883]

[enricocolasante]

Our goal is to have every entity service depending only on its child services and always consider relationships as leaves in the dependency tree.
First step is to remove the dependency on TrackedEntityService, EnrollmentService and EventService that was present in RelationshipOperationParamsMapper and create methods in RelationshipStore to retrieve a single entity of any type using Hibernate.

Next steps

• Migrate and fix commented tests in RelationshipsExportControllerTest
• Move relationship handling into RelationshipService (Remove all getRelationshiItems methods from entity service and centralize them in RelationshipService)
• Pass field params to RelationshipService in order to only retrieve from the DB what is needed
• Check how we should deal with deleted entities in RelationshipService

[sonarqubecloud]

Quality Gate failed

Failed conditions
5 New issues
5 New Code Smells (required ≤ 0)

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