Pass client configuration in 'new_client' function

[volodymyrZotov]

Currently, there is no possibility of configuring httpx.Client when initializing the client using new_client function. The purpose of this issue to add the configuration ability to the new_client function so it would look like this:

def new_client(url: str, token: str, is_async: bool = False, config: httpx.BaseClient) -> Union[AsyncClient, Client]:

The config parameter should be of type httpx.BaseClient so we can pass any options that httpx.Client and httpx.AsyncClient have.