Enable Che-Theia multi-root mode by default for all workspaces

= Multi-root mode by default Some VS Code extensions must run in Multi-root mode. {prod-short} sets the Multi-root mode for all new workspaces. To turn on the Multi-root mode in workspaces created in an earlier version, set the `multiRoot` parameter in the devfile: [source,yaml] ---- attributes:   multiRoot: 'on' ----