update default config also updates model

[mwdchang]

Summary

This PR does two things

• Allows default configuration to be changed
• When changing default config, the change is propagated into the model. This introduces a refreshing bug where model's description page is not refreshed properly. I think rather than trying to force a workaround here, we should just wait for the model page refactor/restructure that we plan to solve this, and other issues.

Testing

Open up a model

• Go to the model tab
• Change a parameter's value for Default config
• Refresh the page, note that a) The change is persisting, and b) the Description page reflects the same change