Create cannonical place to register light client interfaces

[colin-axner]

Summary

Currently we register light client interfaces in RegisterInterfaces within the core IBC module set as an sdk module. We should expose some API to register interfaces without adding code to the core IBC module. My first inclination is to add this function to the app module basic, so app.go files will be required to provide a function registering all their desired light clients. An alternative is to use the go init() function

In the short term, chains can simply add a call to the RegisterInterfaces for external light clients within the construction of the App in app.go

Decision

Add a field to AppModuleBasic to register interfaces, the list of functions can be taken in via NewAppModuleBasic. In AppModuleBasic.RegisterInterfaces should iterate over the functions provided

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged/assigned

[colin-axner]

After discussion with @damiannolan we will go with the app module basic approach. IBC clients as SDK modules allows for additional benefits such as having external information (metadata) being controlled outside of 02-client (migrations, genesis). The benefits require SDK intermodule routing, but this is a step in the long term direction that will eventually be needed. I will write an ADR outlining the problems/eventual solution and why the AppModuleBasic approach is aligned in that direction

[colin-axner]

Closed! AppModuleBasics have been added for tendermint and solo machine. #2008 will add documentation to show external devs how to create an app module basic