variant annotations: add witness keys (labeling)

variant witnesses should get following information attached:

{
"id": "ID we are using right now",
"label": "One letter reference",
"title": "Long title"
}

https://projects.academiccloud.de/projects/ahiqar/work_packages/59342/activity

assigned to @mgoebel

created branch 297-variant-annotations-add-witness-keys-labeling to address this issue

mentioned in merge request !314 (merged)

changed the description

mentioned in commit 217fb0b5

closed with merge request !314 (merged)