feat(bigquery): add support to capture schema of nested fields

[anjali9791]

Closes: #462

edit: change refer to closes

[anjali9791]

The http_extractor_test.go failing in plugins-test here is passing on my local. Here is a screenshot for the same.

[sudo-suhas]

Could you change the expectedErr for that test to Error:Field validation for 'url' failed on the 'required' tag? The failure is because of the different ordering between content_type and accept.