fix: serialize whole-object request bodies and accept host_config

[mokevnin]

Ten methods take their request body as one object, but their params models never declared that field, so the SDK sent it as given, in snake_case:

method	field
containers.create	config
configs.create, configs.update	spec
secrets.create, secrets.update	spec
services.create, services.update	spec
nodes.update, swarm.update	spec
volumes.create	create_request

client.containers.create(config: {image: "alpine", exposed_ports: {"80/tcp" => {}}})
# before: {"image":"alpine","exposed_ports":{"80/tcp":{}}}
# after:  {"Image":"alpine","ExposedPorts":{"80/tcp":{}}}

Go decodes JSON field names case-insensitively, so image and cmd happened to work, but every multi-word field (exposed_ports, cpu_shares, …) was silently dropped by Docker.

• Params models: each declares its body field with the model the resource signature already named, so the field is dumped in API names (lib, rbi, rbs).
• containers.create: also takes host_config:, typed with the existing Container::HostConfig. In the Engine API the create body is ContainerConfig plus HostConfig and NetworkingConfig in one object; host_config is merged in as HostConfig. NetworkingConfig has no model in the SDK and is left out.
• Tests: cover the request body of containers.create and secrets.create; both fail before the change.

rake lint (rubocop, Sorbet, Steep) and rake test (184 runs, 0 failures) pass.

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