Add env variable to cmd flags (cosmos#9040)

* first draft

* add tests in config_test package

* refactored, all tests pass, r4r

* ready for review

* add envPrefix

* Update simapp/simd/cmd/root.go

Co-authored-by: Amaury <1293565+amaurym@users.noreply.github.com>

* fix linter issues

* minor fixes

Co-authored-by: Alessio Treglia <alessio@tendermint.com>
Co-authored-by: Amaury <1293565+amaurym@users.noreply.github.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

simd/cmd/root.go

@@ -47,7 +47,7 @@ func NewRootCmd() (*cobra.Command, params.EncodingConfig) {
 		WithAccountRetriever(types.AccountRetriever{}).
 		WithBroadcastMode(flags.BroadcastBlock).
 		WithHomeDir(simapp.DefaultNodeHome).
-		WithViper()
+		WithViper("") // In simapp, we don't use any prefix for env variables.
 
 	rootCmd := &cobra.Command{
 		Use:   "simd",