fix validation issues

[bootsa]

BASE-Search's OVAL OAI-PMH enpoint validator reports issues with the endpoint:

• ERROR: Error during resumption request: Namespace prefix jats on kwd-group is not defined, line 1306, column 55 (line 1306)
• WARNING: Records should at least contain the DC elements: date, creator, identifier, type, title. Found a record (wikidata-Q27724066) missing the following DC element(s): date, creator.

These errors are also present though previously have been disregarded by BASE administrators:

• ERROR: Server accepts only GET requests.
• ERROR: No incremental harvesting (day granularity) of ListRecords: Harvest for reference date 2022-05-14 returned no records. Please make sure that the from and until parameters are evaluated.

[bootsa]

Updated version of the OAI-PMH endpoint php script now supports POST requests - installed and working on server.

The Incremental Harvesting error still appears but @pietsch commented in an email (25.03.2022) that the OVAL Validator tool might falsely report this and that it might not be an issue. Currently there doesn't seem to be any problems harvesting, so closing.