Fix #[16222], Added Model::setRelated()

[rudiservo]

Hello!

• Type: bug fix
• Link to issue: https://github.com/phalcon/cphalcon/issues/16222

In raising this pull request, I confirm the following:

• [X] I have read and understood the Contributing Guidelines
• [X] I have checked that another pull request for this purpose does not exist
• [X] I wrote some tests for this PR
• [X] I have updated the relevant CHANGELOG
• [X] I have created a PR for the documentation about this change

Small description of change: Added Model::setRelated() for those who want to make a setter for relations or avoid magic __set(), changed the magical __set() to use setRelated()

Thanks