* restore .gitmodules

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

This reverts commit 3b050c8b64175c0d26b6bcafcba6c5a68ebf1477.

* revert 3b050c8b64175c0d26b6bcafcba6c5a68ebf1477

* immigrate file change from stand-alone repo to TDengine

for 2.4

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

Subscription implemented
Continuous Query implemented
Fixed bugs when dealing with null values retrieved from tables
Removed unused code
Added basic performance test code