feat!: add app version to param store

[cmwaters]

Description

Ported over from #347

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[evan-forbes]

to double check my understanding, this is a breaking change ofc but it will not be breaking until the app version if > 2, correct?

[cmwaters]

to double check my understanding, this is a breaking change ofc but it will not be breaking until the app version if > 2, correct?

This is the intention. I will be able to test it properly on the celestia-app side

[evan-forbes]

re-approving even tho we don't have to in this repo to indicate that I have reviewed the fix

[rootulp]

[question] where or how does this "set" the app version? The invoked function returns the app version but I don't know what "set" is referring to here.

cosmos-sdk/baseapp/baseapp.go

Lines 208 to 211 in 4c897c6

	// AppVersion returns the application's protocol version.
	func (app *BaseApp) AppVersion() uint64 {
	return app.appVersion
	}

[rootulp]

[not blocking] can these two include an example to help further differentiate them?

If version = 2.0.0 then is appVersion = 2? Is appVersion always expected to be the major version of the version string?

[rootulp]

On re-review, I think it would be helpful if we updated the README w/ a line item for the rationale for this modification