Rename runnables into tasks (#8119)

Release Notes:

- N/A

assets/settings/initial_runnables.json

@@ -1,27 +0,0 @@
-// Static runnables configuration.
-//
-// Example:
-// {
-//     "version": "1",
-//     "runnables": [
-//         {
-//             "label": "human-readable label for UI",
-//             "command": "bash",
-//             // rest of the parameters are optional
-//             "args": ["-c", "for i in {1..10}; do echo \"Second $i\"; sleep 1; done"],
-//             // Env overrides for the command, will be appended to the terminal's environment from the settings.
-//             "env": { "foo": "bar" },
-//             // Current working directory to spawn the command into, defaults to current project root.
-//             "cwd": "/path/to/working/directory",
-//             // Whether to use a new terminal tab or reuse the existing one to spawn the process, defaults to `false`.
-//             "use_new_terminal": false,
-//             // Whether to allow multiple instances of the same runnable to be run, or rather wait for the existing ones to finish, defaults to `false`.
-//             "allow_concurrent_runs": false
-//         }
-//     ]
-// }
-//
-{
-    "version": "1",
-    "runnables": []
-}