[Ruby] Add Flag to Allow Ignoring Operation Servers

[ckoegel]

This change adds a flag to the configuration object to allow for ignoring operation servers. Currently, if operation level server objects are defined, there is no way to ignore these or use a different base path at the SDK level, which many other languages support. The new ignore_operation_servers flag allows the user to ignore any operation servers defined and instead use the currently defined scheme, host, and base_path. This will default to the top level base path defined in the OpenAPI file, but can be configured to be any url using the aforementioned config attributes.

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@cliffano (2017/07) @zlx (2017/09) @autopp (2019/02)

[wing328]

lgtm. let's give it a try

thanks for the PR