Remove Fee from Auth Info, and put Signatures into it

[ValarDragon]

I am looking at the structure of a tx, as described in this file
https://github.com/cosmos/cosmos-sdk/blob/4a1b2fba43b1052ca162b3a1e0b6db6db9c26656/proto/cosmos/tx/v1beta1/tx.proto

This structure is confusing, since it seems that "signer_info" is metadata describing the signature/who it comes from. Confusingly, the "signer info" is not packaged with the signature, and is instead packaged with the fees in a struct called "auth_info". This leads to a very unintuitive structure.

We propose the struct instead be

{
  Body
  Fee
  AuthInfo {
    SignerInfo
    Signatures
  }
}

Auth Info should be Authn depending on the decision in #7615
(Written jointly with @sunnya97 )

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[aaronc]

Have you read through ADR 020 and all the surrounding discussions? Tx is organized the way it is to 1) expose the minimum malleability surface and 2) make client signing implementations as simple as possible. This is not just a code hygiene issue. I don't really feel that it will be productive for us to discuss aesthetics without considering all the other somewhat complex and subtle issues. And considering the quite lengthy discussions we already had, I'm pretty resistant to changing it again without a strong signing workflow or security reason.