Enable getting autoregister organizations from BPA

[amandazhuyilan]

In this pull request, we enable the capability to get the autoregister organizations from BPA Data Portal.

AAI-213: Expose an API endpoint in the aai-backend that returns the list of BPA Data Portal organizations

Changes

• Add services/ckan_client.py
• Add ckan related configs in config.py
• Add related unit tests
• Add _get_bpa_autoregister_list() - this will be used in aai-portal.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)

How to Test Manually (if necessary)

All new unit tests shall pass.

[amandazhuyilan]

Closing this pull request and re-opening in #61