Invenio-rdm-records

- pids: add support for optional DOI

- mappings: add missing `identifiers` to community orgs
* Adds the missing `identifiers` mapping field to community organizations

- bibtex: add trailing comma in url field
- community-records: allow scan search
* Adds `scan` and `scan_params` arguments to
`CommunityRecordsService.search(...)`, to allow for serving scan
results (but only via the service).
- serializer: updated subjects and affiliations in dcat
- schema: added identifiers to subjects
- serializers: add datapackage serializer (1742)

- github: return None for `NOASSERTION` license
- datacite: fix funding serialization for optional award fields
* Makes sure that we handle missing values for optional award fields
like "title" and "number".

- github: handle missing repo license

- github: lower license spdx id