Code cleanup

[briri]

Some leftover cleanup for the Apollo Server backend. Need some of it for the Authentication/Authorization proof of concept

• Fix issue with returning a null error instead of a normal 404 response when contributorRoleId or contributorRoleURL do not return a result
• Fix issue with missing DMP ID base domain
• Add dmsps to return list of DMSPs (need this to test out user auth)
• Add tests