fix: add gravity proposals so they can be decoded (#1213)

# Related Github tickets

- Closes #1832

# Background

We already have gov proposals from the gravity module on chain, so we
need to register them in order for them to be decoded.

We need to add them in the `gravity` proto directory, so the proto file
names match the proto package, otherwise we get warnings on the command
line.

The resulting gravity types reside within the `skyway/types` dir.

# Testing completed

- [x] test coverage exists or has been added/updated
- [x] tested in a private testnet

# Breaking changes

- [x] I have checked my code for breaking changes
- [x] If there are breaking changes, there is a supporting migration.

proto/palomachain/paloma/gravity/bridge_tax_proposal.proto

@@ -0,0 +1,14 @@
+syntax = "proto3";
+package palomachain.paloma.gravity;
+
+import "cosmos_proto/cosmos.proto";
+
+option go_package = "github.com/palomachain/paloma/x/skyway/types/gravity";
+
+message SetBridgeTaxProposal {
+  string title = 1;
+  string description = 2;
+  string rate = 3 [ (cosmos_proto.scalar) = "cosmos.Dec" ];
+  repeated string excluded_tokens = 4;
+  repeated string exempt_addresses = 5;
+}

proto/palomachain/paloma/gravity/bridge_transfer_limit_proposal.proto

@@ -0,0 +1,26 @@
+syntax = "proto3";
+package palomachain.paloma.gravity;
+
+import "gogoproto/gogo.proto";
+
+option go_package = "github.com/palomachain/paloma/x/skyway/types/gravity";
+
+enum LimitPeriod {
+  NONE = 0;
+  DAILY = 1;
+  WEEKLY = 2;
+  MONTHLY = 3;
+  YEARLY = 4;
+}
+
+message SetBridgeTransferLimitProposal {
+  string title = 1;
+  string description = 2;
+  string token = 3;
+  string limit = 4 [
+    (gogoproto.customtype) = "cosmossdk.io/math.Int",
+    (gogoproto.nullable) = false
+  ];
+  LimitPeriod limit_period = 5;
+  repeated string exempt_addresses = 6;
+}

proto/palomachain/paloma/gravity/erc20_to_denom_proposal.proto

@@ -0,0 +1,14 @@
+syntax = "proto3";
+package palomachain.paloma.gravity;
+
+import "cosmos_proto/cosmos.proto";
+
+option go_package = "github.com/palomachain/paloma/x/skyway/types/gravity";
+
+message SetERC20ToDenomProposal {
+  string title = 1;
+  string description = 2;
+  string chain_reference_id = 3;
+  string erc20 = 4;
+  string denom = 5;
+}

x/skyway/types/codec.go

@@ -6,6 +6,7 @@ import (
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/cosmos/cosmos-sdk/types/msgservice"
 	govtypes "github.com/cosmos/cosmos-sdk/x/gov/types/v1beta1"
+	"github.com/palomachain/paloma/x/skyway/types/gravity"
 )
 
 // ModuleCdc is the codec for the module
@@ -36,6 +37,10 @@ func RegisterInterfaces(registry types.InterfaceRegistry) {
 
 	registry.RegisterImplementations(
 		(*govtypes.Content)(nil),
+		// Register the legacy gravity proposals
+		&gravity.SetERC20ToDenomProposal{},
+		&gravity.SetBridgeTaxProposal{},
+		&gravity.SetBridgeTransferLimitProposal{},
 		&SetERC20ToDenomProposal{},
 		&SetBridgeTaxProposal{},
 		&SetBridgeTransferLimitProposal{},