Handle error on duplicating product name

[Jeshan7]

Why?

Same product name was being entered for two different products. At DB level unique constraint is not for the name but, it is for the slug. This uniqueness constraint should be applicable for the products which are not deleted in the system, hence, uniqueness is now checked on a combination on slug name and deleted_at product field.

This change addresses the need by:

Created a unique_index on combination of slug and deleted_at in migrations. Added unique_constraint on slug and deleted_at in product.ex (schema)

[delivers #164069814]

Checklist

• [ ] I have read CONTRIBUTING.md.
• [ ] My code follows the style guidelines of this project.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] My code does not generate any (new) credo and compile-time warnings.
• [ ] I have updated the documentation wherever necessary.
• [ ] I have added tests to cover my changes.

[codecov[bot]]

Codecov Report

Merging #477 into develop will increase coverage by 0.01%. The diff coverage is 75%.

@@             Coverage Diff             @@
##           develop     #477      +/-   ##
===========================================
+ Coverage    79.87%   79.89%   +0.01%     
===========================================
  Files          176      176              
  Lines         2216     2218       +2     
===========================================
+ Hits          1770     1772       +2     
  Misses         446      446

Impacted Files	Coverage Δ
...core/lib/core/tools/elasticsearch/product/store.ex	36.84% <ø> (ø)	:arrow_up:
apps/snitch_core/lib/core/data/model/product.ex	97.24% <ø> (ø)	:arrow_up:
apps/snitch_core/lib/core/data/schema/product.ex	88.23% <75%> (+0.73%)	:arrow_up:

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