Enhance works/publications metadata from OpenAlex

[nuest]

When a new publication is added, we could query OpenAlex for more information, such as additional locations (Open Access versions for example).

Definetely store the OpenAlex ID with every article.

See OpenAlex entities: https://docs.openalex.org/api-entities/entities-overview

Related to #175 #168 #169

[nuest]

expand all harvesting to identify an existing OpenAlex record based on the available unique identifier and store the OpenAlex ID together with the record; if there is no perfet match then the OpenAlex property of the record should be set to "None" and a seperate field should indicate which partial match(es) were found and what kind of match it was (e.g. DOI match, title+author match, etc);

only implement this feature once for all different harvesting variants and content providers;

from the OpenAlex data about works, store the following additional properties in the publication model in fields prefixed with "openalex_": fulltext_origin, is_retracted, ids, keywords (only the display name), open_access (only the status, and "None" if is_oa is False), topics (only the display name);

the OpenAlex ID is used to create clickable link on the work landing page and in the map popup that links to the OpenAlex page of the work;