Added Mission related APIs

Signed-off-by: Nwusongqing <wusongqing@huawei.com>

en/application-dev/reference/apis/js-apis-application-MissionInfo.md

+# MissionInfo
+
+> **NOTE**
+> The initial APIs of this module are supported since API 8.
+
+
+Provides mission information of an ability.
+
+
+## Modules to Import
+
+Import **Want** before use.
+
+
+```
+import Want from "../@ohos.application.Want";
+```
+
+
+## MissionInfo
+
+Describes the mission information.
+
+**System capability**: SystemCapability.Ability.AbilityBase
+
+| Name| Type| Readable| Writable| Description| 
+| -------- | -------- | -------- | -------- | -------- |
+| missionId | number | Yes| Yes| Mission ID.| 
+| runningState | number | Yes| Yes| Running state of the mission.| 
+| lockedState | boolean | Yes| Yes| Locked state of the mission.| 
+| timestamp | string | Yes| Yes| Latest time when the mission was created or updated.| 
+| want | [Want](js-apis-featureAbility.md#want) | Yes| Yes| **Want** information of the mission.| 
+| label | string | Yes| Yes| Label of the mission.| 
+| iconPath | string | Yes| Yes| Path of the mission icon.| 
+| continuable | boolean | Yes| Yes| Whether the mission is continuable.| 

en/application-dev/reference/apis/js-apis-application-MissionSnapshot.md

+# MissionSnapshot
+
+
+> **NOTE**
+> The initial APIs of this module are supported since API 8.
+
+
+Provides snapshot of a mission.
+
+
+## Modules to Import
+
+Import ElementName and image before use.
+
+
+```
+import { ElementName } from '../bundle/elementName';
+import { image } from '../@ohos.multimedia.image';
+```
+
+
+## MissionSnapshot
+
+Describes the mission snapshot.
+
+  | Name| Type| Readable| Writable| Description|
+| -------- | -------- | -------- | -------- | -------- |
+| ability | ElementName | Yes| Yes| Information that matches an ability.|
+| snapshot | [image.PixelMap](js-apis-image.md) | Yes| Yes| Snapshot of the mission.|