doc: OVN and Amphora mixed in the text

The page describes both OVN and Amphora providers. It is kind of clear at the beginning how to enable each but the section which describes how to check LB works is not clear. In LB create it specifically says to use --provider but later SOURCE_IP_PORT algorithm is used which is only for OVN.
Also the very first lb create command shows operating_state ONLINE while my amphora showed OFFLINE (maybe different issue and maybe ovn vs amphora)

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Document: how-to/features/load-balancer.rst