[FEATURE] Better scale handling through recOrder CLI

[talonchandler]

@ieivanov @ziw-liu had a short discussion about our long-term goals for recOrder's scale handling. We agreed that we'd like to trust the input store's scale metadata if it exists, and we'd like the option to override that metadata from the config file if needed.

We considered either yx_pixel_size: None or 'read-from-input' for the overriding behavior, and I'm happy with either.

Related discussion: #419