Merge intent controller actions

[elia]

Summary

Merge the two actions in the intent controller, they follow mostly the same behavior with a single deviation depending on the type of intent.

Ref #210

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[elia]

For later, does add_to_wallet seem like something that could belong to the strategy class?

@kennyadsl we could only if we rely on it for deciding which kind of intent we expect, instead of reacting to the presence of the param (e.g. param[:payment_intent]).

[elia]

Merging, since the failure is related to the starter frontend and is already being fixed by @rainerdema 🙌