Read Work identifiers from file

This is taking the same steps applied to editions[1] and authors[2] and
applying it to works. `get_work_config()` is currently not used for
anything, probably because we’re still waiting for an actual interface
to edit the Work identifiers[3], so this is more a preliminary step to
ensure that Works will be handled in the same way that Editions and
Authors are. (And to allow for PRs to add Work identifiers while waiting
for that UI.)

[1] #9234
    #9483
[2] #9666
    #9769
[3] #3430

openlibrary/plugins/openlibrary/config/work/identifiers.yml

@@ -0,0 +1,22 @@
+identifiers:
+-   label: BookBrainz
+    name: bookbrainz
+    url: https://bookbrainz.org/work/@@@
+    website: https://bookbrainz.org
+-   label: Книга Файнфиков
+    name: ficbook
+    notes: ''
+    url: https://ficbook.net/readfic/@@@
+-   label: MusicBrainz
+    name: musicbrainz
+    url: https://musicbrainz.org/work/@@@
+    website: https://musicbrainz.org
+-   label: MyAnimeList
+    name: myanimelist
+    notes: ''
+    url: https://myanimelist.net/manga/@@@
+-   label: Wikidata
+    name: wikidata
+    notes: ''
+    url: https://www.wikidata.org/wiki/@@@
+    website: https://wikidata.org

openlibrary/plugins/upstream/utils.py

@@ -1264,6 +1264,32 @@ def _get_edition_config():
     )
 
 
+@public
+def get_work_config() -> Storage:
+    """Returns the work config.
+
+    This just calls _get_work_config(). See that
+    function's documentation for further details.
+    """
+    return _get_work_config()
+
+
+@web.memoize
+def _get_work_config() -> Storage:
+    """Returns the work config.
+
+    The results are cached on the first invocation.
+    The /config/work page currently has no unique options so we
+    don't load/fetch it here currently.
+    """
+    with open('openlibrary/plugins/openlibrary/config/work/identifiers.yml') as in_file:
+        id_config = yaml.safe_load(in_file)
+        identifiers = [
+            Storage(id) for id in id_config.get('identifiers', []) if 'name' in id
+        ]
+    return Storage(identifiers=identifiers)
+
+
 from openlibrary.core.olmarkdown import OLMarkdown