feat(8-kyu): kata/multiply-the-number

kata/8-kyu/multiply-the-number/README.md

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+# [Multiply the number](https://www.codewars.com/kata/multiply-the-number "https://www.codewars.com/kata/5708f682c69b48047b000e07")
+
+Jack really likes his number five: the trick here is that you have to multiply each number by 5 raised to the number of
+digits of each number, so, for example:
+
+```
+Kata.multiply(3) == 15      // 3 * 5¹
+Kata.multiply(10) == 250    // 10 * 5²
+Kata.multiply(200) == 25000 // 200 * 5³
+Kata.multiply(0) == 0       // 0 * 5¹
+Kata.multiply(-3) == -15    // -3 * 5¹
+```

kata/8-kyu/multiply-the-number/main/Kata.java

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+interface Kata {
+  static int multiply(int number) {
+    return number * (int) Math.pow(5, (int) (Math.log10(Math.abs(number)) + 1));
+  }
+}

kata/8-kyu/multiply-the-number/test/MultiplyExampleTests.java

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+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class MultiplyExampleTests {
+  @Test
+  void sample() {
+    assertEquals(-15, Kata.multiply(-3));
+    assertEquals(0, Kata.multiply(0));
+    assertEquals(15, Kata.multiply(3));
+    assertEquals(250, Kata.multiply(10));
+    assertEquals(25000, Kata.multiply(200));
+    assertEquals(-3728750, Kata.multiply(-5966));
+    assertEquals(-2048000000, Kata.multiply(-131072));
+  }
+}