docs: create v2 upgrading guide

UPGRADING_v2.md

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+# Upgrading Cosmos SDK v2.x.y
+
+This guide provides instructions for upgrading to specific versions of Cosmos SDK.
+Note, always read the **SimApp** section for more information on application wiring updates.
+
+## Upgrading from v0.52.x to v2.0.0
+
+First and foremost, v2 uses [depinject](./depinject/README.md) to wire the module and application dependencies. This guides assumes you have already made your modules depinject compatible, and that you made use of depinject in your application.
+
+### Modules
+
+* sdk.Context to core service migration: https://hackmd.io/@julienrbrt/S16-_Vq50
+* AnteHandler to TxValidator
+* Optional migration from grpc services to handlers
+* [Documentation]: Module configuration #22371
+
+### Server
+
+TODOs:
+
+* Telemetry server is another port (1328)
+* New REST server for querying modules (8080) -> Use post and type_url (docs at server/v2/api/rest/README.md)
+* gRPC: new service to query the modules gRPC messages, without going via module services
+* gRPC: external gRPC services no more registered in the application router (e.g. nodeservice, cmtservice, authtx service)
+
+### SimApp
+
+With the migration to server/v2 and runtime/v2 some changes are required in the `root.go` and `app.go` of your application.
+
+#### `app.go`
+
+#### `root.go`
+
+## Upgrading from v0.50.x to v2.0.0
+
+Upgrading directly from v0.50.x to v2.0.0 is supported.
+Modules should be updated to support all the latest changes in the SDK.
+
+Read the module section from the v0.52 [UPGRADING.md](UPGRADING.md) file for more information.
+Then simply follow the instructions from the [v0.52 section](#upgrading-from-v052x-to-v200) from this file.