feat: support distinct in federated search

src/main/java/com/meilisearch/sdk/MultiSearchFederation.java

@@ -11,6 +11,7 @@ public class MultiSearchFederation {
     private Integer offset;
     private MergeFacets mergeFacets;
     private Map<String, String[]> facetsByIndex;
+    private String distinct;
 
     public MultiSearchFederation setLimit(Integer limit) {
         this.limit = limit;
@@ -32,6 +33,11 @@ public MultiSearchFederation setFacetsByIndex(Map<String, String[]> facetsByInde
         return this;
     }
 
+    public MultiSearchFederation setDistinct(String distinct) {
+        this.distinct = distinct;
+        return this;
+    }
+
     /**
      * Method that returns the JSON String of the MultiSearchFederation
      *

src/test/java/com/meilisearch/sdk/MultiSearchFederationTest.java

@@ -0,0 +1,28 @@
+package com.meilisearch.sdk;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.not;
+
+import com.meilisearch.sdk.exceptions.MeilisearchException;
+import com.meilisearch.sdk.json.GsonJsonHandler;
+import org.junit.jupiter.api.Test;
+
+class MultiSearchFederationTest {
+
+    private final GsonJsonHandler jsonHandler = new GsonJsonHandler();
+
+    @Test
+    void serializesDistinctInFederationOptions() throws MeilisearchException {
+        MultiSearchFederation federation = new MultiSearchFederation().setDistinct("movie_id");
+
+        assertThat(jsonHandler.encode(federation), containsString("\"distinct\":\"movie_id\""));
+    }
+
+    @Test
+    void omitsDistinctWhenNotSet() throws MeilisearchException {
+        MultiSearchFederation federation = new MultiSearchFederation().setLimit(10);
+
+        assertThat(jsonHandler.encode(federation), not(containsString("distinct")));
+    }
+}