* restore .gitmodules for 2.0

* Revert "[TD-13408]<test>: move tests out from TDengine"

This reverts commit 9d342bf3f5b404fc1014400060e012b387bfdb8c.

* immigarate file change from stand-alone repo to TDengine

for 2.0

* remove tests repository checkout
Co-authored-by: Ntangfangzhi <fztang@taosdata.com>

Connector is implemented by lua51 but luajit and ffi are not included. Connection pool is not implemented yet. It is a raw demonstration at present and not verified on production environment.