Add database dictionary support for deleted tables/views

Context:

Instead of hard-coding deleted tables and views in Gitlab::Database::GitlabSchema::DELETED_TABLES, we should have a place in the dictionary where we put them. We can add a new folder to the dictionary called deleted where developers move deleted tables and views.

Definition of done:

• Add deleted tables and views to the database dictionary
• Load deleted tables/views gitlab schemas from the database dictionary
• Change documentation
• Remove DELETED_TABLES from (Gitlab::Database::GitlabSchema)

cc @DylanGriffith @OmarQunsulGitlab @alexives @ayufan