Unit test for `api_collector`

[klesh]

Description

Now we have 400 lines of code for api_collector, it become quite complicated and error-prone, plus, we have already found multiple bugs during v0.10 testing.

Describe the solution you'd like

Build an unit-test for api_collector to cover all possible routes with mocking github.com/stretchr/testify/mock techinque.
IMPORTANT: should not be any actual database operation / api request get performed when running test-cases

Has the Feature been Requested Before?

• https://github.com/merico-dev/lake/issues/1665
• https://github.com/merico-dev/lake/issues/1766