Simplify cosmos client construction

[yoshuawuyts]

This PR builds on #884 to slim down the instantiation of the cosmos client. It does away with CosmosOptions and adds more lenient bounds on the constructor. This PR is best reviewed on a per-commit basis. Thanks!

Example

// before
let client = CosmosClient::new(
    account.clone(),
    authorization_token,
    CosmosOptions::default(),
);

// after
let client = CosmosClient::new(&account, authorization_token);

Details

The CosmosOptions struct is a thin wrapper around the azure_core::ClientOptions struct. It doesn't expose any custom fields, and forwards all calls directly to the internal ClientOptions struct.

CosmosOptions has two constructors: the empty new method /Default implementation, and the new_with_transaction_name method. The latter which is only used inside the CosmosClient::new_with_transaction method, so removing it hasn't removed any existing functionality.

We know that we want to expose the ability to add custom pipeline plugins (middleware) to the clients. But this can be done by exposing builder methods on the client, and we don't need an Options struct to achieve this. On the contrary: the work in this PR is intended as prep work to enable the implementation of a builder structure.

So to summarize: no existing functionality is lost, and this sets us up to implement pipeline extensions using builder methods on the client.