Given two sorted lists of integers, write a function to merge them into a single sorted list. The input lists will already be sorted in ascending order. You need to return a new sorted list that contains all elements from both input lists.

Example:

Input:

list1 = [1, 3, 5, 7]
list2 = [2, 4, 6, 8]

Output:
[1, 2, 3, 4, 5, 6, 7, 8]

The two lists are merged into a single sorted list, which contains all elements from both lists in ascending order.