Move `projects` to `gitlab_main_cell` schema

What does this MR do and why?

This is related to #415204 (closed).

We are currently moving cell-local tables to the gitlab_main_cell schema. projects is one of the tables that should be cell local, and in this MR we are moving projects to the gitlab_main_cell schema, and also marking any cross-joins and foreign key migrations originating from projects

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Related to #415204 (closed)