Implement draft pull request related APIs (#2388)

src/main/scala/gitbucket/core/api/ApiPullRequest.scala

@@ -21,7 +21,8 @@ case class ApiPullRequest(
   body: String,
   user: ApiUser,
   labels: List[ApiLabel],
-  assignee: Option[ApiUser]
+  assignee: Option[ApiUser],
+  draft: Option[Boolean]
 ) {
   val id = 0 // dummy id
   val html_url = ApiPath(s"${base.repo.html_url.path}/pull/${number}")
@@ -62,7 +63,8 @@ object ApiPullRequest {
       body = issue.content.getOrElse(""),
       user = user,
       labels = labels,
-      assignee = assignee
+      assignee = assignee,
+      draft = Some(pullRequest.isDraft)
     )
 
   case class Commit(sha: String, ref: String, repo: ApiRepository)(baseOwner: String) {

src/main/scala/gitbucket/core/api/CreateAPullRequest.scala

@@ -5,7 +5,8 @@ case class CreateAPullRequest(
   head: String,
   base: String,
   body: Option[String],
-  maintainer_can_modify: Option[Boolean]
+  maintainer_can_modify: Option[Boolean],
+  draft: Option[Boolean]
 )
 
 case class CreateAPullRequestAlt(

src/main/scala/gitbucket/core/controller/api/ApiPullRequestControllerBase.scala

@@ -114,7 +114,7 @@ trait ApiPullRequestControllerBase extends ControllerBase {
                       requestBranch = reqBranch,
                       commitIdFrom = commitIdFrom.getName,
                       commitIdTo = commitIdTo.getName,
-                      isDraft = false,
+                      isDraft = createPullReq.draft.getOrElse(false),
                       loginAccount = context.loginAccount.get,
                       settings = context.settings
                     )

src/test/scala/gitbucket/core/api/ApiSpecModels.scala

@@ -520,6 +520,7 @@ object ApiSpecModels {
        |"user":$jsonUser,
        |"labels":[$jsonLabel],
        |"assignee":$jsonUser,
+       |"draft":true,
        |"id":0,
        |"html_url":"http://gitbucket.exmple.com/octocat/Hello-World/pull/1347",
        |"url":"http://gitbucket.exmple.com/api/v3/repos/octocat/Hello-World/pulls/1347",