Add index meta to meta table

internal/core/src/pb/CMakeLists.txt

internal/core/src/pb/etcd_meta.pb.cc

internal/core/src/pb/etcd_meta.pb.h

internal/core/src/pb/index_builder.pb.cc

internal/core/src/pb/index_builder.pb.h

internal/master/meta_table.go

internal/master/meta_table_test.go

internal/master/runtime_stats.go

internal/proto/etcd_meta.proto

internal/proto/etcdpb/etcd_meta.pb.go

internal/util/typeutil/index.go

internal/util/typeutil/index_test.go