fix: refactoring endpoint for creating an email to meet c# standard

[sparkybug]

Description

Refactored create email endpoint to match C# docs. ​

Related Issue (Link to Github issue)

https://github.com/hngprojects/hng_boilerplate_nestjs/issues/1053 ​

Motivation and Context

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How Has This Been Tested?

It has been tested on postman and also via unit tests ​

Screenshots (if appropriate - Postman, etc):

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Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change) ​

  Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.