👽 : add JsonProperty to isAdmin field

isAdmin field was serialized as "admin" in Json with previous versions
of jackson-databind
with the newest version, it is serialized as "isAdmin", which does not
seem correct, so adding @JsonProperty to force serialization to correct
field

src/main/java/io/gaia_app/organizations/bo.kt

@@ -17,6 +17,7 @@ data class User(
         @Id val username: String,
         @DBRef val organization: Organization?) {
 
+    @JsonProperty("admin")
     var isAdmin: Boolean = false
 
     var oAuth2User: OAuth2User? = null