Support for Connection String

Hi,

please add support for commands which require a connection string like mysql or sqlplus.

Excample for executorMap:
```
{
"code-runner.executorMap": {
"oracle": "sqlplus $connectString @$fullFileName"
}
}
```

If a command in the executorMap contains the variable $connectString, the user will be prompted to enter the login data (for sqlplus: username/password@host)

It might be usefull, if you can configure a list of connect strings for each executorMap entry.
This configuration should be stored in the Workspace settings or a separeate file.