Add email format validation

[volcodes]

Implement email format validation to ensure that user-provided email addresses adhere to standard formatting rules. This validation will improve data integrity and prevent invalid email addresses from being stored in the database or processed by the application.

Acceptance Criteria:

• Create a utility function to validate email format using a regular expression that complies with the RFC 5322 standard or equivalent.
• Integrate the validation function into the user registration and update workflows.
• Provide appropriate error messages when an invalid email format is detected.
• Write unit tests to cover various valid and invalid email formats.
• Ensure that all existing functionality is unaffected by this addition.

Technical Notes:

• Consider using regexp from the standard Go library for email format validation.
• Avoid overly complex regex patterns to maintain readability and efficiency.
• Follow existing error-handling patterns for a consistent codebase.

Priority: Medium
Labels: Validation, Backend, Go