Generates Web API documentation programmatically with extra tests

Description

I introduced swagger-ui-py to generate Web API documentation from our OpenAPI configuration.

Besides, I added a heartbeat endpoint for testing purposes, with manual tests run for /ping and /data endpoints.

The repository doc is also added as a sub-module due to the necessity of documentation generation.

I removed unnecessary artifacts which are challenging to update. Their functionalities are replaced by swagger-ui-py.

Item	Is checked?	Description
Explanation	O	My changes are well-explained.
Documentation	O	My works are well-commented or clear.
Tests	O	I have added tests or reports to cover my changes.