Add ssl mode prompt.

[lvegerano]

Augments the changes to Borvik/vscode-postgres#35.

It essentially allow you to set the connection ssl mode.

[Borvik]

Setting the "defaults" seems iffy to me. That might affect other connections. I was thinking of trying to set connectionOptions.ssl to boolean true, and if there was a file then an object with the file details like normal. Some research leads me to think that will probably work. I also might tweak the add connection steps, so that the cert choice only is asked if ssl was selected.

[lvegerano]

You may be right that this may affect other connections. I really did not tested another db connection. I was under the assumption that each connection has a new instance of pg. I will test this out.