Add Batch Email Sending Functionality to Mailtrap Gem

[ryush00]

The Mailtrap gem supports bulk server functionality but lacks batch email sending. I’d like to suggest adding this feature using the https://bulk.api.mailtrap.io/api/batch endpoint. This aligns with the Mailtrap bulk API documentation.

[mklocek]

Thanks @ryush00 for your request. It makes sense and this feature is in our backlog