Add challenge stars

[tschaffter]

Related to Sage-Bionetworks/rocc-schemas#164

[coveralls]

Pull Request Test Coverage Report for Build 1236170985

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 187 unchanged lines in 12 files lost coverage.
• Overall coverage decreased (-0.7%) to 44.057%

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Files with Coverage Reduction	New Missed Lines	%
openapi_server/models/response_page_metadata.py	2	38.0%
openapi_server/controllers/auth_controller.py	4	32.26%
openapi_server/models/page_of_challenge_platforms.py	5	41.54%
openapi_server/models/page_of_challenges.py	5	41.54%
openapi_server/models/page_of_grants.py	5	41.54%
openapi_server/models/page_of_organizations.py	5	41.54%
openapi_server/models/page_of_org_memberships.py	5	41.54%
openapi_server/models/page_of_persons.py	5	41.54%
openapi_server/models/page_of_tags.py	5	41.54%
openapi_server/models/page_of_users.py	5	41.54%

Totals
Change from base Build 1234685738:	-0.7%
Covered Lines:	1338
Relevant Lines:	3037

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💛 - Coveralls