Added the ability to change thumbnails of sticker sets created by the bot using the method setStickerSetThumb

Author: pengrad

library/src/main/java/com/pengrad/telegrambot/request/SetStickerSetThumb.java

@@ -0,0 +1,21 @@
+package com.pengrad.telegrambot.request;
+
+import com.pengrad.telegrambot.response.BaseResponse;
+
+/**
+ * Stas Parshin
+ * 31 March 2020
+ */
+public class SetStickerSetThumb extends AbstractUploadRequest<AddStickerToSet, BaseResponse> {
+
+    public SetStickerSetThumb(String name, Integer userId, Object thumb) {
+        super(BaseResponse.class, "thumb", thumb);
+        add("name", name);
+        add("user_id", userId);
+    }
+
+    public SetStickerSetThumb(String name, Integer userId) {
+        super(BaseResponse.class, "name", name);
+        add("user_id", userId);
+    }
+}

library/src/test/java/com/pengrad/telegrambot/TelegramBotTest.java

@@ -156,6 +156,7 @@
 import com.pengrad.telegrambot.request.SetGameScore;
 import com.pengrad.telegrambot.request.SetMyCommands;
 import com.pengrad.telegrambot.request.SetStickerPositionInSet;
+import com.pengrad.telegrambot.request.SetStickerSetThumb;
 import com.pengrad.telegrambot.request.SetWebhook;
 import com.pengrad.telegrambot.request.StopMessageLiveLocation;
 import com.pengrad.telegrambot.request.StopPoll;
@@ -296,6 +297,7 @@ public static TelegramBot createTestBot() {
     static String gifFileId = "CgADAgADfQADgNqgSTt9SzatJhc3FgQ";
     static String withSpaceFileId = "BAADAgADZwADkg-4SQI5WM0SPNHrAg";
     static String stickerSet = "testset_by_pengrad_test_bot";
+    static String stickerSetAnim = "testset_anim_by_pengrad_test_bot";
     static String imageUrl = "https://telegram.org/img/t_logo.png";
     static File thumbFile = resourcePath.resolve("thumb.jpg").toFile();
     static byte[] thumbBytes;
@@ -1389,6 +1391,17 @@ public void deleteStickerFromSet() {
         }
     }
 
+    @Test
+    public void setStickerSetThumb() {
+        String thumbFile = "CAACAgIAAxkBAAJ0ll6DO4bNCynpfZmS6g-YcGY2zrP5AAIBAAPANk8TGC5zMKs_LVEYBA";
+        BaseResponse response = bot.execute(new SetStickerSetThumb(stickerSetAnim, chatId, thumbFile));
+        assertTrue(response.isOk());
+
+        // clear thumb by not sending it
+        response = bot.execute(new SetStickerSetThumb(stickerSetAnim, chatId));
+        assertTrue(response.isOk());
+    }
+
     @Test
     public void editMessageLiveLocation() {
         BaseResponse response = bot.execute(new EditMessageLiveLocation(chatId, 10009, 21, 105)