Issue/Pull expose IsLocked Property on API (#11708)

Expose IsLocked Property

modules/convert/issue.go

 		Body:     issue.Content,
 		Labels:   ToLabelList(issue.Labels),
 		State:    issue.State(),
+		IsLocked: issue.IsLocked,
 		Comments: issue.NumComments,
 		Created:  issue.CreatedUnix.AsTime(),
 		Updated:  issue.UpdatedUnix.AsTime(),

modules/convert/pull.go

 		Assignee:  apiIssue.Assignee,
 		Assignees: apiIssue.Assignees,
 		State:     apiIssue.State,
+		IsLocked:  apiIssue.IsLocked,
 		Comments:  apiIssue.Comments,
 		HTMLURL:   pr.Issue.HTMLURL(),
 		DiffURL:   pr.Issue.DiffURL(),

modules/structs/issue.go

 	// type: string
 	// enum: open,closed
 	State    StateType `json:"state"`
+	IsLocked bool      `json:"is_locked"`
 	Comments int       `json:"comments"`
 	// swagger:strfmt date-time
 	Created time.Time `json:"created_at"`

modules/structs/pull.go

 	Assignee  *User      `json:"assignee"`
 	Assignees []*User    `json:"assignees"`
 	State     StateType  `json:"state"`
+	IsLocked  bool       `json:"is_locked"`
 	Comments  int        `json:"comments"`
 
 	HTMLURL  string `json:"html_url"`

templates/swagger/v1_json.tmpl

           "format": "int64",
           "x-go-name": "ID"
         },
+        "is_locked": {
+          "type": "boolean",
+          "x-go-name": "IsLocked"
+        },
         "labels": {
           "type": "array",
           "items": {
           "format": "int64",
           "x-go-name": "ID"
         },
+        "is_locked": {
+          "type": "boolean",
+          "x-go-name": "IsLocked"
+        },
         "labels": {
           "type": "array",
           "items": {