Add public interface for multistore to return earlist version (#525)

## Describe your changes and provide context
This PR add a public interface for Multistore to return the earlist
available version for state store (historical state). For seidb, if only
SC is enabled, then it will assume only latest state is available.

## Testing performed to validate your change

server/mock/store.go

@@ -257,3 +257,8 @@ func (ms multiStore) SetKVStores(handler func(key store.StoreKey, s sdk.KVStore)
 func (ms multiStore) StoreKeys() []sdk.StoreKey {
 	panic("not implemented")
 }
+
+func (ms multiStore) GetEarliestVersion() int64 {
+	//TODO implement me
+	panic("not implemented")
+}

store/cachemulti/store.go

@@ -241,3 +241,7 @@ func (cms Store) Close() {
 		closer.Close()
 	}
 }
+
+func (cms Store) GetEarliestVersion() int64 {
+	panic("not implemented")
+}

store/rootmulti/store.go

@@ -61,6 +61,7 @@ type Store struct {
 	pruneHeights        []int64
 	initialVersion      int64
 	archivalVersion     int64
+	earliestVersion     int64
 	orphanOpts          *iavltree.Options
 
 	traceWriter       io.Writer
@@ -526,6 +527,9 @@ func (rs *Store) PruneStores(clearStorePruningHeights bool, pruningHeights []int
 			}
 		}
 	}
+	if len(pruningHeights) > 0 {
+		rs.earliestVersion = pruningHeights[len(pruningHeights)-1]
+	}
 
 	if clearStorePruningHeights {
 		rs.pruneHeights = make([]int64, 0)
@@ -1217,3 +1221,7 @@ func (rs *Store) StoreKeys() []types.StoreKey {
 	}
 	return res
 }
+
+func (rs *Store) GetEarliestVersion() int64 {
+	return rs.earliestVersion
+}

store/types/store.go

@@ -121,6 +121,9 @@ type MultiStore interface {
 	GetStore(StoreKey) Store
 	GetKVStore(StoreKey) KVStore
 
+	// Get the earliest available version for state store
+	GetEarliestVersion() int64
+
 	// TracingEnabled returns if tracing is enabled for the MultiStore.
 	TracingEnabled() bool
 

storev2/rootmulti/store.go

@@ -854,10 +854,23 @@ func (*Store) SetKVStores(handler func(key types.StoreKey, s types.KVStore) type
 }
 
 // StoreKeys implements types.CommitMultiStore.
-func (s *Store) StoreKeys() []types.StoreKey {
-	res := make([]types.StoreKey, len(s.storeKeys))
-	for _, sk := range s.storeKeys {
+func (rs *Store) StoreKeys() []types.StoreKey {
+	res := make([]types.StoreKey, len(rs.storeKeys))
+	for _, sk := range rs.storeKeys {
 		res = append(res, sk)
 	}
 	return res
 }
+
+// GetEarliestVersion return earliest version for SS or latestVersion if only SC is enabled
+func (rs *Store) GetEarliestVersion() int64 {
+	latestVersion := rs.lastCommitInfo.Version
+	if rs.ssStore != nil {
+		version, err := rs.ssStore.GetEarliestVersion()
+		if err != nil {
+			return latestVersion
+		}
+		return version
+	}
+	return latestVersion
+}