Additional email options

[Curicows]

First of all, thanks for the project it's amazing and I'm using it self-hosted like a charm.
I only had one small issue that I think might be interesting to be add.

While deploying my self-hosted Solidtime using Docker, I was setting up the MAIL configuration (I use MailerSend) and I can't add it because the "MailerSend" option wasn't added to the config mail in the Laravel config file:

While checking the Laravel documentation about Mail drivers available, I come across multiple available drivers (some needs to just install a connector Composer package) that isn't available to be used in the Solidtime deploy.

It would the awesome to get the others mail drivers available to anyone that is deploying the application self-hosted.

Thanks for the attention. <3