feat(email_sender): add max size to the attachments

Feature/Implement Maximum Attachment Size for Email Messages

Description

This pull request introduces a new feature that allows setting a maximum size for attachments in EmailMessage instances within the gomail package. The feature includes:

A default maximum attachment size of 25 MB.
A method to set a custom maximum attachment size.
Logic to exclude attachments that exceed the specified maximum size during the email sending process.
Comprehensive updates to the documentation to describe the new feature and provide instructions on its usage.

This enhancement improves the usability and reliability of the gomail package by preventing large attachments from causing email delivery failures. It aligns with best practices for email transmission and assists users in avoiding common issues.

Related Issue: Closes #11
Type of Change:
- New feature (non-breaking change which adds functionality)

Checklist

Please ensure the following guidelines are met:

[x] The code follows the style guidelines of this project.
[x] A self-review has been performed on the code.
[x] The code is well-documented, and comments have been added where necessary.
[x] Tests have been added to prove that the fix is effective or that the feature works. All existing tests pass.
[x] Commit messages follow the convention type(scope): description.
[x] The pull request has no conflicts with the base branch.
[x] Any dependent changes have been merged and published in downstream modules.

Additional Information

This feature will enhance the usability and reliability of the gomail package by preventing large attachments from causing email delivery failures. The implementation includes comprehensive tests to ensure the feature works as intended and does not introduce regressions. The documentation has been updated to reflect these changes and provide guidance on using the new functionality.

darkrockmountain / gomail