Improve `send_email.py` for Enhanced Security, Consistency, and Flexibility

[smog-root]

The current implementation of send_email.py works well for sending basic emails, but there are a few areas for improvement. These changes will enhance security, consistency, and flexibility in the email-sending functionality. Suggested Improvements

I'm expecting gssoc-ext with a level and hacktoberfest-accepted labels!! @UTSAVS26

1. Fix Typo in Docstring:

• Update recepient_mail to recepient_email in the docstring under Args to match the function parameter.

2. Improve Security by Avoiding Hardcoded Credentials:

• Replace hardcoded credentials with environment variables. This will prevent sensitive information from being exposed in the code.
• Update the if name == "main": block to load credentials from environment variables instead.

3. Allow HTML Formatting in Email Body:

• Add an optional parameter to specify the email content type (e.g., "plain" or "html").
• Modify the code to support HTML content in the email body if specified.

4. Add Network Error Handling:

• Enhance error handling by catching network-related errors, such as connection timeouts, to provide better feedback when email sending fails.

5. Add Type Hints:

• Add type hints to the function parameters and return type for better readability and to leverage type checking.

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