Use radian

[mthomas-ketchbrook]

Radian provides an R console with autocomplete / suggestions in a way that we currently do not have in place. See the installRadian option in https://github.com/rocker-org/devcontainer-features/blob/main/src/r-apt/README.md.

Additionally, the following VSCode settings should be updated in devcontainer.json:

// ...
"vscode": {
	"settings": {
		// # other VSCode settings like ruler, etc.
		"terminal.integrated.profiles.linux": {
                	"bash": {
                	    "path": "/bin/bash",
                	    "icon": "terminal-bash"
                	},
                	"radian": {
                	    "path": "/usr/local/bin/radian",
                	    "icon": "graph"
                	}
            	},
		"r.rterm.linux": "/usr/local/bin/radian"  // make extensions like R debugger play nicely with radian
	},
//...