Create 'An introduction to depinject' tutorial

[julienrbrt]

• Create An introduction to depinject tutorial (probably under https://docs.cosmos.network/main/building-modules)
  The tutorial should explain how to use depinject with AppConfig for building modules (wait until the API is stabilized and depinject tagged and released) and more generally the application configuration (with examples).

Raw structure (feel free to edit):

 # An introduction to `AppConfig`
## What is dependency injection
## How to use `depinject`
## Migrate a module

• Follow-up on docs(depinject): clarify depinject API #12214 for improving the README (or link to the tutorial).

• Explain how to use app wiring with a module (creation of the module.proto)

[julienrbrt]

Should we add this back in the Sprint? I can go back to this.