[ActionPack] Add deep_transform_keys to ActionController::StrongParameters

We are currently working with Rails API interacting with a frontend app. In order to simplify the interactions with the front app, we are supporting parameters and responses with camelCase.

When we were implementing this in the Rails API, we encountered that ActionController::StrongParameters implements transform_keys but it doesn’t implements deep_transform_keys, as Hash does.

This would be a helpful feature for us because we use nested params for some requests, and we think it would also make the StrongParams API more similar to the Hash API.

Any feedback on this would be very helpful. In AcidTango we have the intention to implement this feature if it is considered helpful.


:+1: for this method.Can you open the PR?

Yes, will start working in a PR.

Opened the PR here.