The GlobalBlockLookup service needs to read the value of gb_create_account and then apply this to the GlobalBlock instances that it returns. This so that the block can be optionally set to apply to account creation.
This is safe to do so now because the column exists on WMF wikis (T371415) and a default is set for this column of 1 which will ensure that the current behaviour (all global blocks prevent account creation) continues to apply.
Acceptance criteria
- Update GlobalBlockLookup to read the value from the gb_create_account column and use it / return it where necessary.