[Feature]: Add configuration flag to support migration from store/v1 -> store/v2

[kocubinski]

Summary

There is no out of the box migration support from store/v1 -> store/v2 for a server/2 app.

Problem Definition

The store/v2 root store factory does not support migration manager set up, the argument is always set as nil.

cosmos-sdk/store/v2/root/factory.go

Line 180 in 325728a

return New(opts.Logger, ss, sc, pm, nil, nil)

Proposed Feature

Extend the store/v2/root.Config options with a boolean flag to enable migration if set.

cosmos-sdk/store/v2/root/config.go

Lines 10 to 14 in 325728a

	type Config struct {
	Home string `toml:"-"` // this field is omitted in the TOML file
	AppDBBackend string `mapstructure:"app-db-backend" toml:"app-db-backend" comment:"The type of database for application and snapshots databases."`
	Options Options `mapstructure:"options" toml:"options"`
	}

This flag should be ignored in TOML, but settable from simapp/v2/app_di.go so that the feature is configuration is chain wide by default, not node specific.

[julienrbrt]

From last API review call, it was said it would be nice to improve the migration UX by not requiring to turn on/set migrator manually.