papis: Add papis-tag tag-listing command

Command takes a query and lists all the tags contained in
all documents of the query sorted alphabetically.

writing/.config/papis/scripts/papis-tags

@@ -0,0 +1,39 @@
+#!/usr/bin/env python
+# papis-short-help: List all tags occuring in query items
+#
+# Takes a query and spits out a sorted list of all tags contained therein,
+# nothing more.
+# Can be very useful for things like picking a tag or two and listing all
+# items that contain it:
+# $ papis tags "*" | fzf | xargs papis show "tags:{}"
+
+import argparse
+from papis import database
+from papis.database.base import Database
+
+from papis.document import Document
+
+parser = argparse.ArgumentParser()
+parser.add_argument("query", nargs="*", help="the query to search for")
+args = parser.parse_args()
+
+
+def main(db: Database, args) -> None:
+    query = " ".join(args.query)
+    docs: list[Document] = db.query(query)
+
+    all_tags: set[str] = set()
+    for doc in docs:
+        t: list[str] | str = doc.get("tags", "")
+        tags = (
+            t.replace(";", ",").replace(" ", "").split(",") if isinstance(t, str) else t
+        )
+
+        for tag in tags:
+            all_tags.add(tag)
+
+    for tag in sorted(all_tags):
+        print(tag)
+
+if __name__ == "__main__":
+    main(database.get(), args)