fix(SPV-1283): use proper upsertcontact command field for a path param

[wregulski]

This pull request includes changes to the contacts feature to improve the handling of paymail addresses. The most important changes include the addition of a new field for contact paymail and updates to the relevant methods and tests to reflect this change.

Handling of Paymail Addresses:

• commands/contacts.go: Added a new field ContactPaymail to the UpsertContact struct to separately store the paymail address of the contact being added or updated. Updated the field name Paymail to RequesterPaymail for clarity.
• examples/contact_upsert/contact_upsert.go: Updated the example to use the new ContactPaymail field and provided comments for the optional RequesterPaymail field.
• internal/api/v1/user/contacts/contacts_api.go: Modified the UpsertContact method to use the new ContactPaymail field when making the HTTP PUT request.
• internal/api/v1/user/contacts/contacts_api_test.go: Updated the test for the UpsertContact method to use the RequesterPaymail field.

Pull Request Checklist

• 📖 I created my PR using provided : CODE_STANDARDS
• 📖 I have read the short Code of Conduct: CODE_OF_CONDUCT
• 🏠 I tested my changes locally.
• ✅ I have provided tests for my changes.
• 📝 I have used conventional commits.
• 📗 I have updated any related documentation.
• 💾 PR was issued based on the Github or Jira issue.

[github-actions]

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