Persistent SSH session

A lot of users of our Julia extension love the remote SSH features, they are super useful in a scientific research computing context!

One thing that has come up a lot lately, though, is that folks want an ability to have a persistent session on a server that they can disconnect from and then reconnect to way later.

The scenario is essentially something like this:

1. User connects to some remote server via the Remote SSH extension
2. They do some work
3. They get interrupted and close their local VS Code instance
4. They do something else for a couple of days
5. The now want to reconnect to the server, and ideally nothing was shut down on the server. For example, if they opened a REPL in step 2 and started a Julia instance in that REPL, it would still be running, and was never shut down. Similarly with pretty much all other runtime state they had.

I think this might be related to https://github.com/microsoft/vscode-remote-release/issues/440, but what I'm really asking for is not just an option to change the timeout, but some way to make the timeout infinit, so that the server session never shuts down.

This might also require some kind of UI, maybe a command like "Disconnect but keep server alive" or something like that, not sure.

Start by reading the Remote SSH extension behavior described in this issue and the related issue #440; the payload names no files or tests. Done means a user can disconnect from VS Code, reconnect days later, and find the remote server and runtime state, such as a Julia REPL, still alive.