We now have change tag data starting from September 2018 in the Data Lake (T201062), but we still need older tag data in the same schema so it can be easily unioned (T205932). Product-Analytics will take care of getting it into the proper schema if the raw data can be loaded into the Data Lake.
We only need a one-time sqoop to do this, but we might as well add this to the normal mediawiki_history sqoop since we'll ultimately need that for T161149.
There is a refactor of the change_tag tables underway (T185355), but the new ct_tag_id columns and change_tag_def tables are actually already being written, so as long as we avoid select * from change_tag, we won't have to change the workflow again.
Essentially, what we want sqooped is:
SELECT database(), ct_rev_id, ct_tag_id, ctd_name, FROM change_tag LEFT JOIN change_tag_def ON ct_tag_id = ctd_id