Add check_sponsor method to Partner resource

With this endopoint we can check if a partner can sponsor new partners. Using the sponsor_code and the vat we can found the partner and check if has more slots to sponsor.

assigned to @danypr92

By Daniel Palomar on 2022-04-11T16:12:33 (imported from GitLab)

added 2 commits

• 2a37ffc9 - Fix Partner assertions
• f99984be - Add message to check_sponsor method in Partner resource

Compare with previous version

By Daniel Palomar on 2022-04-20T09:31:33 (imported from GitLab)

added 1 commit

• 1356e850 - Add message to check_sponsor method in Partner resource

Compare with previous version

By Daniel Palomar on 2022-04-20T09:53:58 (imported from GitLab)

mentioned in commit 799a11da

By Daniel Palomar on 2022-04-20T09:59:34 (imported from GitLab)