feat: validate email according to RFC 5322

[NeatGuyCoding]

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Summary

This PR updates the email validation function in the EmailChangeModal component to comply with RFC 5322 standards. The change replaces the basic email regex pattern with a more comprehensive RFC 5322-compliant regex pattern and adds a length validation to ensure email addresses don't exceed 254 characters.

Changes made:

• Updated email validation regex from a simple pattern to RFC 5322 compliant pattern
• Added email length validation (max 254 characters) as per RFC specifications
• Enhanced validation to support more valid email address formats including special characters allowed by RFC 5322

Motivation:
The previous email validation was too restrictive and didn't follow RFC 5322 standards, potentially rejecting valid email addresses. This update ensures better compatibility with legitimate email formats while maintaining security.

Screenshots

Before	After
Basic email regex validation with limited character support	RFC 5322 compliant validation with comprehensive character support and length validation

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods