According to https://wikitech.wikimedia.org/wiki/Schema_changes#What_is_not_a_schema_change we should block on DBA review when creating new tables.
Dear DBAs, please review the new table we're adding in https://gerrit.wikimedia.org/r/c/mediawiki/extensions/OAuthRateLimiter/+/613282/9/schema/oauth_ratelimit_client_tier.sql
The table will only be present on OAuth central wiki, and will hold a mapping 'client_id' -> 'client_tier_name'. It's a one-to-one relationship. The tier name is an arbitrary string, currently listed in the config, but in future we might add an extra table to hold tier name -> tier config mappings.
We do not put the ratelimit tier into the oauth_client table because this is not a native oauth concept, thus the code for supporting it was extracted to a separate extension, and storage is extracted into a separate table.