New field for ID for works in collection.yaml

Works can be identified using IDs from GND or Wikidata. We want to keep this information in the TG-metadata files. For that, we need a new field in the collection.yaml file. It can be the last element in the section for the work (see "id (neues Feature)" in #22 (comment 1264110)). As in the other cases, we need the possibility of assigning this information as fixed value or through an xpath that searches this information in the TEI file. Several values are possible (see following example).

The information needs to go in the work.meta file, in the provided element. Currently, the workflow produces the following output:

        <provided>
            <title>Exodus (Chinese)</title>
            <format>text/tg.work+xml</format>
        </provided>

We need to produce this:

        <provided>
            <title>Exodus (Chinese)</title>
            <format>text/tg.work+xml</format>
            <identifier type="URL">https://d-nb.info/gnd/4015988-7</identifier>
            <identifier type="URL">https://www.wikidata.org/wiki/Q9190</identifier>
        </provided>

In this case, we do need the entire URL. So, no regex or splitting should be applied (in contrast to what we do here #23 (closed))