Integrate mailhog into our container matrix integration tests

[todvora]

If we want to be able to test and validate our mail infrastructure, we need to integrate some kind of mail server in our testing infrastructure.

This PR adds an instance of https://github.com/mailhog/MailHog to our testcontainers setup and provides basic utils to search and obtain received messages.

How Has This Been Tested?

Added integration test

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Refactoring (non-breaking change)
• [ ] 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.