Validate Custom SuffixCreate customDOIAvail, add documentation, call in validateSUFFIX,...
- customDOIAvail takes a custom suffix and returns true if it is available for use, false otherwise
- is called in validateSUFFIX, a method for the frontend to call when a user inputs a custom suffix (1st validation step)
- is also called in publishManuscript prior to calling publishToGoogleDocs and publishToCrossRef (2nd validation step)