feat: Add Tips middleware (#10208)

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## Description

R4R

Closes: #9912 

This PR introduces 1 new middleware:
- `TipsMiddleware`: transfer tip from tipper to feePayer when relevant.

It also makes sure in the DIRECT_AUX sign mode handler that the fee payer cannot use that sign mode.

Depends on:
- [x]  #10028 
- [x] #10268 
- [x] #10322 
- [x] #10346 

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---

### Author Checklist

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please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

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your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

types/tx/aux.go

@@ -48,6 +48,23 @@ func (a *AuxSignerData) ValidateBasic() error {
 	return a.GetSignDoc().ValidateBasic()
 }
 
+// GetSignaturesV2 gets the SignatureV2 of the aux signer.
+func (a *AuxSignerData) GetSignatureV2() (signing.SignatureV2, error) {
+	pk, ok := a.SignDoc.PublicKey.GetCachedValue().(cryptotypes.PubKey)
+	if !ok {
+		return signing.SignatureV2{}, sdkerrors.ErrInvalidType.Wrapf("expected %T, got %T", (cryptotypes.PubKey)(nil), pk)
+	}
+
+	return signing.SignatureV2{
+		PubKey: pk,
+		Data: &signing.SingleSignatureData{
+			SignMode:  a.Mode,
+			Signature: a.Sig,
+		},
+		Sequence: a.SignDoc.Sequence,
+	}, nil
+}
+
 // UnpackInterfaces implements the UnpackInterfaceMessages.UnpackInterfaces method
 func (a *AuxSignerData) UnpackInterfaces(unpacker codectypes.AnyUnpacker) error {
 	return a.GetSignDoc().UnpackInterfaces(unpacker)

types/tx/aux_test.go

@@ -6,6 +6,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	codectypes "github.com/cosmos/cosmos-sdk/codec/types"
+	cryptotypes "github.com/cosmos/cosmos-sdk/crypto/types"
 	"github.com/cosmos/cosmos-sdk/testutil/testdata"
 	"github.com/cosmos/cosmos-sdk/types/tx"
 	"github.com/cosmos/cosmos-sdk/types/tx/signing"
@@ -77,6 +78,12 @@ func TestAuxSignerData(t *testing.T) {
 				require.Error(t, err)
 			} else {
 				require.NoError(t, err)
+				sigV2, err := tc.sd.GetSignatureV2()
+				require.NoError(t, err)
+				require.Equal(t, tc.sd.Mode, sigV2.Data.(*signing.SingleSignatureData).SignMode)
+				require.Equal(t, tc.sd.Sig, sigV2.Data.(*signing.SingleSignatureData).Signature)
+				require.Equal(t, tc.sd.SignDoc.Sequence, sigV2.Sequence)
+				require.True(t, tc.sd.SignDoc.PublicKey.GetCachedValue().(cryptotypes.PubKey).Equals(sigV2.PubKey))
 			}
 		})
 	}