docs: adding migration doc info for sdk v0.47 (backport #3107) (#3156)

Co-authored-by: Damian Nolan <[email protected]>
Co-authored-by: Colin Axnér <[email protected]>

docs/migrations/v6-to-v7.md

@@ -168,11 +168,11 @@ if err := clientState.VerifyMembership(
 
 The `GetRoot` function has been removed from consensus state interface since it was not used by core IBC.
 
-### Client Keeper
+### Client keeper
 
 Keeper function `CheckMisbehaviourAndUpdateState` has been removed since function `UpdateClient` can now handle updating `ClientState` on `ClientMessage` type which can be any `Misbehaviour` implementations.  
 
-### SDK Message
+### SDK message
 
 `MsgSubmitMisbehaviour` is deprecated since `MsgUpdateClient` can now submit a `ClientMessage` type which can be any `Misbehaviour` implementations.
 
@@ -290,4 +290,62 @@ import (
 
 - host.RouterKey
 + ibcexported.RouterKey
-```
+```
+
+## Upgrading to Cosmos SDK 0.47
+
+The following should be considered as complementary to [Cosmos SDK v0.47 UPGRADING.md](https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc2/UPGRADING.md).
+
+### Protobuf 
+
+Protobuf code generation, linting and formatting have been updated to leverage the `ghcr.io/cosmos/proto-builder:0.11.5` docker container. IBC protobuf definitions are now packaged and published to [buf.build/cosmos/ibc](https://buf.build/cosmos/ibc) via CI workflows. The `third_party/proto` directory has been removed in favour of dependency management using [buf.build](https://docs.buf.build/introduction).
+
+### App modules
+
+Legacy APIs of the `AppModule` interface have been removed from ibc-go modules. For example, for 
+
+```diff
+- // Route implements the AppModule interface
+- func (am AppModule) Route() sdk.Route {
+-     return sdk.Route{}
+- }
+-
+- // QuerierRoute implements the AppModule interface
+- func (AppModule) QuerierRoute() string {
+-     return types.QuerierRoute
+- }
+-
+- // LegacyQuerierHandler implements the AppModule interface
+- func (am AppModule) LegacyQuerierHandler(*codec.LegacyAmino) sdk.Querier {
+-     return nil
+- }
+-
+- // ProposalContents doesn't return any content functions for governance proposals.
+- func (AppModule) ProposalContents(_ module.SimulationState) []simtypes.WeightedProposalContent {
+-     return nil
+- }
+```
+
+### Imports
+
+Imports for ics23 have been updated as the repository have been migrated from confio to cosmos.
+
+```diff
+import (
+    // ...
+-   ics23 "github.com/confio/ics23/go"
++   ics23 "github.com/cosmos/ics23/go"
+    // ...
+)
+```
+
+Imports for gogoproto have been updated.
+
+```diff
+import (
+    // ...
+-   "github.com/gogo/protobuf/proto"
++   "github.com/cosmos/gogoproto/proto"
+    // ...
+)
+```