As a content editor I want to add or edit labels for blocks of transcription text so that I can indicate new sections or different kinds of texts.

[rlskoeser]

testing notes (qa)

After testing #911, confirm:

• You can add/edit a label in a separate text box from the annotation body
• Labels persist after saving, and are properly deleted along with a deleted annotation
• labels are optional

dev notes

• determine how/where to store labels in the annotation object (tag or special metadata)
• store label on the annotation text (annotation.resource.label)
• update tahqiq to add optional field for editing/adding labels
• populate label with existing value when present
• ensure storage plugin persists label when converting between v2 / v3 annotations

[richmanrachel]

Works! Closing :)