feat: As a user, I want to count unique attested subjects

[alainncls]

What does this PR do?

1. Adds a script to get all attestations and save all the subjects in files
2. Adds a script to count unique subjects

Related ticket

Fixes #475

Type of change

• Chore
• Bug fix
• New feature
• Documentation update

Check list

• Unit tests for any smart contract change
• Contracts and functions are documented

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0e7288e) 93.63% compared to head (8e2dc90) 93.63%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #466   +/-   ##
=======================================
  Coverage   93.63%   93.63%           
=======================================
  Files          20       20           
  Lines         330      330           
  Branches       76       76           
=======================================
  Hits          309      309           
  Misses         10       10           
  Partials       11       11           

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