make annotation motivation consistent & configurable

[rlskoeser]

dev notes

• make sure tei migration and tahqiq are generating annotation motivations the same way
• tahqiq secondary motivation should be configurable so we can adapt for translation later
• should keep "supplementing" as primary motivation
• motivation should be stored at top level of annotation body (motivation on the content body is redundant unless there are multiple different content sections, e.g. if we added support for tags and kept them in the same annotation with transcription content)

[rlskoeser]

confirmed on the test site that new annotations are created with the correct motivation