Add migration to make some foreign key names consistent

What does this MR do and why?

The database diagnostics page identified a number of missing foreign keys, but they actually exist in other names. It appears that these inconsistencies occurred for a number of reasons:

1. ActiveRecord automatically generates foreign keys in the form of fk_rails_<hash>, but during the squashing of migrations these foreign keys got renamed to fk_<hash>. This commit adds a migration to rename known foreign keys back to fk_rails_<hash> again.

2. Some indexes were not renamed when their respective tables were renamed. <hash> is calculated with the original table name. This commit adds a migration to rename the foreign keys using the hash with the new table name.

References

https://gitlab.com/gitlab-com/request-for-help/-/issues/3342

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