Default client-side `alpha` for hybrid queries should be removed

[databyjp]

Currently there is a default alpha value on the client-side queries. This should be removed on the client-side in favour of a server-side default.

In parallel, we are investigating how the server-side default is implemented for gRPC calls to ensure parity with the GraphQL interface. Internal slack discussion: https://weaviate-org.slack.com/archives/C07ATH510BF/p1722351635163289?thread_ts=1722347271.735859&cid=C07ATH510BF

[tsmith023]

Core PR that allows sending alpha_param as UNSET: weaviate/weaviate#10553

This issue should include the change to use alpha_param instead of alpha