Multiple minors fix and improve

use data class for entity
Add sealed on entity interfaces
Replace listOf() by setOf() instead of deduplicate
use interface instead of EntityRef
replace .toLowerCase() to .lowercase()
fix test.sh

src/test/kotlin/integration/steps/given/Workgroup.kt

@@ -62,7 +62,7 @@ private fun createWorkgroup(
     val creatorName = createdBy ?: CitizenI.Name("Paul", "Langevin")
     val creator = citizenRepository.findByName(creatorName) ?: run {
         val username = ("username" + UUID.randomUUID().toString())
-            .toLowerCase().replace(' ', '-')
+            .lowercase().replace(' ', '-')
         val user = UserForCreate(
             username = username,
             password = "Azerty123!",