feat: only update the app version when at 0

[cmwaters]

Description

This is a minor change after testing out the upgrade process using celestia-app.

It fixes the bug of using the passed version instead of ctx.BlockHeader().Version.App

It also only loads the appVersion parameter from disk once upon startup (which is when the Info method is called)

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[evan-forbes]

mind elaborating on the purpose of this?

[cmwaters]

We should only load the app version once which is when it's set to 0 as opposed to loading from disk every time Info is called