Expose tls parameter of Go MySQL driver to config file (#855)

Co-authored-by: Jonas Gunz <himself@jonasgunz.de>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/855
Reviewed-by: konrad <konrad@kola-entertainments.de>
Co-authored-by: kompetenzbolzen <himself@jonasgunz.de>
Co-committed-by: kompetenzbolzen <himself@jonasgunz.de>

docs/content/doc/setup/config.md

@@ -237,6 +237,12 @@ Secure connection mode. Only used with postgres.
 
 Default: `disable`
 
+### tls
+
+Enable SSL/TLS for mysql connections. Options: false, true, skip-verify, preferred
+
+Default: `false`
+
 ---
 
 ## cache