feature: add a priority field to match routes with the same path in the order of priority.

Expected result, the second routing rule matches first.

```lua
{
    {
        paths = {"/aa*"},
        metadata = "metadata /aa",
        priority = 0
    },
    {
        paths = {"/aa*"},
        metadata = "metadata /aa",
        hosts = {"foo.com"},
        priority = 100
    }
}
```