Refactor delegate endpoint signatures to use EIP712

[Uxio0]

Currently we require to sign a hash, which is really wrong, and we should refactor the delegate signature to use an EIP712, similar to what we do for the delete transactions endpoint.

[mjadach-iv]

Duplicate of /v1/delegates/ hash to sign by a Safe owner is very scary and undescriptive #1857

[JagoFigueroa]

Looks good to me after checking with Felipe. I have left the checks for the v1 endpoints to the mobile team as a staging build of the app is needed to verify that delegation is working as expected.

Cheers