Define a sharding key for group_wiki_repository_states

Table group_wiki_repository_states should meet the guidelines for sharding so it can be linked to an Organization: https://docs.gitlab.com/development/organization/#defining-a-sharding-key-for-all-organizational-tables

When the work is complete, the new column should fulfil the following criteria:

• has no default
• is not nullable
• has a foreign key to organizations