Make references searchable

[lcanobbio]

Description of feature
Make the reference field in contributiones searchable in cv-search as well. It should work exactly the same way as when searching for another field that is already searchable.

Additional context
Make sure that the reference field can also be filtered in the dropdown under the category Contribution once this feature is merged.

• Feature/1145 add section specific dropdown to cv search #1173

TODO

• references can be found in the cv-search
• Tests
• Update CHANGELOG.md if feature is major
• Update Readme.md if necessary