題目敘述
題目會給定一個pandas DataFrame作為輸入，要求我們以原有的資料表為基礎，融合不同的資料欄位。
以product作為index，融合quarter_1,quarter_2,quarter_3,quarter_4 這四個欄位，並且重新命名為quarter，並且將數值欄位名稱重新命名為sales。
測試範例
Example 1:
Input:
+-------------+-----------+-----------+-----------+-----------+
| product | quarter_1 | quarter_2 | quarter_3 | quarter_4 |
+-------------+-----------+-----------+-----------+-----------+
| Umbrella | 417 | 224 | 379 | 611 |
| SleepingBag | 800 | 936 | 93 | 875 |
+-------------+-----------+-----------+-----------+-----------+
Output:
+-------------+-----------+-------+
| product | quarter | sales |
+-------------+-----------+-------+
| Umbrella | quarter_1 | 417 |
| SleepingBag | quarter_1 | 800 |
| Umbrella | quarter_2 | 224 |
| SleepingBag | quarter_2 | 936 |
| Umbrella | quarter_3 | 379 |
| SleepingBag | quarter_3 | 93 |
| Umbrella | quarter_4 | 611 |
| SleepingBag | quarter_4 | 875 |
+-------------+-----------+-------+
Explanation:
The DataFrame is reshaped from wide to long format. Each row represents the sales of a product in a quarter.
以product作為index，融合quarter_1,quarter_2,quarter_3,quarter_4 這四個欄位，並且重新命名為quarter，
並且將數值欄位名稱重新命名為sales。
