Allow specifying more than one server names in the get_tools call of MultiServerMCPClient

While calling `get_tools` on an instance of the `MultiServerMCPClient`, we can specify only one server name. However, there may be situations where we want to get the tools from more than one server, e.g., filter a list of connections based on transport type. Thus, an implementation for `async def get_tools(self, *, server_names: list[str] | None = None) -> list[BaseTool]` would be nice to have.