Golang Insert At Index (any slice)
array1 := []int{1, 3, 4, 5}
array2 := []int{2, 4, 6, 8}
array1 = append(array1, 0) // Step 1
copy(array1[2:], array1[1:]) // Step 2
array1[1] = array2[2] // Step 3
fmt.Println(array1)
// Output
// [1 6 3 4 5]