Deprecate MergeRequest#mergeStatus (#885)

Co-authored-by: Jérémie Bresson <dev@jmini.fr>

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

@@ -36,7 +36,13 @@ public class MergeRequest {
     private Date latestBuildStartedAt;
     private String mergeCommitSha;
     private String squashCommitSha;
+    /**
+     * @deprecated since 15.6, use {@link #detailedMergeStatus} instead.
+     * see https://docs.gitlab.com/ee/update/deprecations.html#merge_status-api-field
+     */
+    @Deprecated
     private String mergeStatus;
+    private String detailedMergeStatus;
     private Date mergedAt;
     private Participant mergedBy;
     private Boolean mergeWhenPipelineSucceeds;
@@ -273,14 +279,30 @@ public class MergeRequest {
         this.squashCommitSha = squashCommitSha;
     }
 
+    /**
+     * @deprecated since 15.6, use {@link #getDetailedMergeStatus()} instead.
+     */
+    @Deprecated
     public String getMergeStatus() {
         return mergeStatus;
     }
 
+    /**
+     * @deprecated since 15.6, use {@link #setDetailedMergeStatus(String)} instead.
+     */
+    @Deprecated
     public void setMergeStatus(String mergeStatus) {
         this.mergeStatus = mergeStatus;
     }
 
+    public String getDetailedMergeStatus() {
+        return detailedMergeStatus;
+    }
+
+    public void setDetailedMergeStatus(String detailedMergeStatus) {
+        this.detailedMergeStatus = detailedMergeStatus;
+    }
+
     public Date getMergedAt() {
         return mergedAt;
     }

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

@@ -6,6 +6,7 @@
     "project_id":3,
     "title":"test1",
     "state":"merged",
+    "detailed_merge_status": "can_be_merged",
     "upvotes":0,
     "downvotes":0,
     "created_at": "2016-12-03T17:23:34Z",