Show `devTasks` and allow launching them.

[fabioz]

i.e.: I would like to launch "Validate Users" from extension but can't:

devTasks:
  Validate file structure:
    robotTaskName: Validate File Structure

[fabioz]

@mikahanninen

[kariharju]

This issue has been moved here, under Sema4AI/vscode-extension repository.