Use a chain config for testing package chain setup

[colin-axner]

Summary

Add a new ChainConfig struct to create custom testing chains

Problem Definition

The testing pkg originally was intended for internal usage, but quickly external developers forked ibc-go to access the testing pkg. It was then redesigned and extended to allow app developer to make use of the package. They can do this by overiding the DefaultTestingAppInit variable in the testing package. The intention was that this would only need to be overriden once.

With more complex workflows, we see app developers wanting to run the testing pkg against two chains configured with different app.go's. See #3286

Proposal

Create a ChainConfig struct:

type ChainConfig struct {                                          
    chainID  string                                              
    appSetup func() (TestingApp, map[string]json.RawMessage)   
}    

This can then be used in NewCoordinator and eventually passed down into SetupWithGenesisValSet. This avoids using a global and allows for a cleaner API as the NewCoordinator call may look like this:

ibctesting.NewCoordinator(t, []ibctesting.ChainConfig{gaiaChainConfig, osmosisChainConfig})

---

For Admin Use

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

[colin-axner]

May or may not be useful if we remove the coordinator, we can revisit after the majority of the testing pkg improvements are in place. Maybe we could provide the config to NewTestChain instead