HTTP API documentation +fix when updating a playlist (#12612)

* get id from path param when updating a playlist

* add playlist http api documentation

* remove required condition for the id in update cmd

pkg/api/playlist.go

@@ -160,6 +160,7 @@ func CreatePlaylist(c *m.ReqContext, cmd m.CreatePlaylistCommand) Response {
 
 func UpdatePlaylist(c *m.ReqContext, cmd m.UpdatePlaylistCommand) Response {
 	cmd.OrgId = c.OrgId
+	cmd.Id = c.ParamsInt64(":id")
 
 	if err := bus.Dispatch(&cmd); err != nil {
 		return Error(500, "Failed to save playlist", err)

pkg/models/playlist.go

@@ -63,7 +63,7 @@ type PlaylistDashboards []*PlaylistDashboard
 
 type UpdatePlaylistCommand struct {
 	OrgId    int64             `json:"-"`
-	Id       int64             `json:"id" binding:"Required"`
+	Id       int64             `json:"id"`
 	Name     string            `json:"name" binding:"Required"`
 	Interval string            `json:"interval"`
 	Items    []PlaylistItemDTO `json:"items"`