Only save composed expansion params

[paynejd]

Right now expansion params save whatever a user specified in a request and all defaults. Instead, expansion parameters should be treated as composed content, meaning that we only save the params that a user explicitly requested. Defaults should be silently applied rather than saved with the expansion. If I view an expansion's details, I should only see the params that I provided. This does not need to be applied retroactively.

[snyaggarwal]

@paynejd this is deployed on QA and Staging
Existing expansion parameters are also migrated to save only non-default values.