feat(users): add email to MergeIdentifier object

[antonioturdo]

🚨 Proposed changes

Add email and prioritization to MergeIdentifier object according to https://www.braze.com/docs/api/endpoints/user_data/post_users_merge/

⚙️ Types of changes

What types of changes does your code introduce? Put an x in the boxes that apply

• New feature (non-breaking change which adds functionality)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)
• Refactor

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.57%. Comparing base (51b1810) to head (7b98f47).

Additional details and impacted files

@@            Coverage Diff            @@
##               main      #56   +/-   ##
=========================================
  Coverage     99.57%   99.57%           
- Complexity      494      500    +6     
=========================================
  Files           139      139           
  Lines           939      947    +8     
=========================================
+ Hits            935      943    +8     
  Misses            4        4           

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