Fix Slug Unique Constraint

[Z3d0X]

Fixes: #134

ref: #133

[what-the-diff]

PR Summary

• Revamp Unique Constraints on 'pages' Table
  The introduction of a new migration file eases the alteration of the 'pages' table in the database. Instead of the 'slug' column by itself, the 'slug' paired with 'parent_id' is now uniquely identified, offering more precision when dealing with page data.

• Service Provider File Enhancement
  The update to the 'FilamentFabricatorServiceProvider.php' file improves the handling of database migrations. The newly implemented 'hasMigrations' method adds more flexibility to the configuration, facilitating the addition of 'create_pages_table' and 'fix_slug_unique_constraint_on_pages_table' migrations for effective database handling.