UN-2281: get finance suppliers

[Kariamos]

No description provided.

[github-actions]

Tests difference:

New Tests

< GET /campaigns/campaignId/finance/supplier - Should return 200 if logged in as admin
< GET /campaigns/campaignId/finance/supplier - Should return 403 if logged in as not admin user
< GET /campaigns/campaignId/finance/supplier - Should return 403 if logged out
< GET /campaigns/campaignId/finance/supplier - Should return 403 if no access to the campaign
< GET /campaigns/campaignId/finance/supplier - Should return finance suppliers - admin
< GET /campaigns/campaignId/finance/supplier - Should return suppliers - olp permissions

[coveralls]

coverage: 79.497% (+0.01%) from 79.483%
when pulling 23cf049 on UN-2281-get-finance-suppliers
into 1cedfdc on UN-2274-other-costs.