feat: SSH Tunnel functionality

[digitalgopnik]

Uses ssh2-promise for tunnel-functionality:

See also: ssh2-promise on github

• Fixed also lint-error in not related (src/renderer/scss/themes/dark-theme.scss) - hopefully that's ok in this case. Otherwise pipelines will fail.

Tested with cases:

• local mariadb (with and without ssl)
• local postgres (without ssl)
• ssh mariadb (without ssl) - with ssh-password | ssh-private-key
• ssh postgres (without ssl - with ssh-password | ssh-private-key

[Fabio286]

Hello @digitalgopnik ,
Infinitely thank you for your contribution!
Everything seems to be working fine.

[digitalgopnik]

Great! :) You are welcome!