Add helper eg /data/ol_dump_editions_latest.txt.gz links for ratings/readinglog

[cdrini]

Work towards #3989 .

Technical

Testing

$ curl https://testing.openlibrary.org/data/ol_dump_ratings_latest.txt.gz -s -L -I -o /dev/null -w '%{url_effective}'
https://ia601503.us.archive.org/26/items/ol_dump_2021-08-11/ol_dump_ratings_2021-08-11.txt.gz

$ curl https://testing.openlibrary.org/data/ol_dump_reading-log_latest.txt.gz -s -L -I -o /dev/null -w '%{url_effective}'
https://ia801503.us.archive.org/26/items/ol_dump_2021-08-11/ol_dump_reading-log_2021-08-11.txt.gz

$ curl https://testing.openlibrary.org/data/ol_dump_editions_latest.txt.gz -s -L -I -o /dev/null -w '%{url_effective}'
https://ia801503.us.archive.org/26/items/ol_dump_2021-08-11/ol_dump_editions_2021-08-11.txt.gz

$ curl https://testing.openlibrary.org/data/ol_dump_editions_2021-08-11.txt.gz -s -L -I -o /dev/null -w '%{url_effective}'
https://ia801503.us.archive.org/26/items/ol_dump_2021-08-11/ol_dump_editions_2021-08-11.txt.gz

Screenshot

Stakeholders