Add mergeUser to MergeRequest (gitlab4j#910)

Fixes gitlab4j#889

Author: jmini

src/main/java/org/gitlab4j/api/models/MergeRequest.java

@@ -44,7 +44,12 @@ public class MergeRequest {
     private String mergeStatus;
     private String detailedMergeStatus;
     private Date mergedAt;
+    /**
+     * @deprecated since 14.7, use {@link #mergeUser} instead.
+     * see https://docs.gitlab.com/ee/update/deprecations.html#merged_by-api-field
+     */
     private Participant mergedBy;
+    private Participant mergeUser;
     private Boolean mergeWhenPipelineSucceeds;
     private String mergeError;
     private Milestone milestone;
@@ -311,14 +316,32 @@ public void setMergedAt(Date mergedAt) {
         this.mergedAt = mergedAt;
     }
 
+    /**
+     * @deprecated since 14.7, use {@link #getMergeUser()} instead.
+     * see https://docs.gitlab.com/ee/update/deprecations.html#merged_by-api-field
+     */
+    @Deprecated
     public Participant getMergedBy() {
         return mergedBy;
     }
 
+    /**
+     * @deprecated since 14.7, use {@link #setMergeUser(Participant)} instead.
+     * see https://docs.gitlab.com/ee/update/deprecations.html#merged_by-api-field
+     */
+    @Deprecated
     public void setMergedBy(Participant mergedBy) {
         this.mergedBy = mergedBy;
     }
 
+    public Participant getMergeUser() {
+        return mergeUser;
+    }
+
+    public void setMergeUser(Participant mergeUser) {
+        this.mergeUser = mergeUser;
+    }
+
     public Boolean getMergeWhenPipelineSucceeds() {
         return mergeWhenPipelineSucceeds;
     }

src/test/resources/org/gitlab4j/api/merge-request.json

@@ -21,6 +21,14 @@
         "avatar_url": "https://www.google.com/",
         "web_url": "https://www.google.com/"
     },
+    "merge_user": {
+        "id": 87854,
+        "name": "Douwe Maan",
+        "username": "DouweM",
+        "state": "active",
+        "avatar_url": "https://gitlab.example.com/uploads/-/system/user/avatar/87854/avatar.png",
+        "web_url": "https://gitlab.com/DouweM"
+    },
     "merge_error": "Merge request is not mergeable",
     "author":{
         "id":1,