Support query parameter authentication

[duckontheweb]

In the Radiant MLHub API, we use a key query string parameter to pass user API keys as part of our requests. It looks like pystac-client supports adding headers to every request for a Client instance, but I did not see a way to do the same for a query string parameter.

Would you be open to adding a params argument to StacApiIO, Client.open, and Client.file to allow users to include specific query parameters in every request to that API?