chore(server): clean mail-templates and add tailwind style

[hitech95]

With this commit I wanted to complete the react-mail structure by properly define the templates styles by including tailwind css framework.

The framework is extended by both react-mail and tailwindcss-preset-email. Those packages help the rendering for various email clients.

If in future there is the necessity to target specific mail clients the package tailwindcss-email-variants and tailwindcss-mso can help too. The latter has some workarounds for the Ms Outlook that is still lacking a lot of the CSS3 funcitonality. to target