move v2 related constants to v2 directory

[ninabarbakadze]

Summery

          [blocking][question] for @cmwaters. The breakdown of files in `pkg/appconsts` has me wondering where this constant should be defined. Candidates:

1. consensus_consts.go because this is a new "consensus constant"
2. v2/app_consts.go because this is a new param introduced in app version v2

If we do keep this in initial_consts.go then I think we need to update the comment at the top of this file because this constant can't be modified via on-chain governance or the node's local config.

// The following defaults correspond to initial parameters of the network that can be changed, not via app versions
// but other means such as on-chain governance, or the nodes local config

Originally posted by @rootulp in #2985 (comment)