refactor of fee middleware REST urls

[crodriguezvega]

Description

Opening this to discuss if we should adopt this format for the URLs that is closer to the format already in use in existing endpoints.

closes: #XXXX

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[chatton]

LGTM thanks for updating this to keep things consistent. 👍

[damiannolan]

Agree with the proposed changes, I think it makes more sense from a general REST design perspective! Thanks @crodriguezvega 🙌