Add unit test for .add() and .query() function

[deshraj]

Currently, it looks like there are no tests for embedchain python package. Adding basic test case for now that tests the .add() and .query() class for now.

Test results:

(base) ➜  embedchain git:(add-basic-test) pytest
====================================================================================== test session starts ======================================================================================
platform darwin -- Python 3.8.8, pytest-6.2.3, py-1.10.0, pluggy-0.13.1
rootdir: /Users/deshrajyadav/Projects/embedchain
plugins: anyio-3.7.0
collected 2 items                                                                                                                                                                               

tests/test_embedchain.py ..                                                                                                                                                               [100%]

======================================================================================= 2 passed in 2.42s =======================================================================================

[taranjeet]

Good initiative @deshraj . Merged PR.