fix: update virtualenv building so llamastack- prefix is not added, make notebook experience easier (#1225)

Make sure venv behaves like conda (no prefix is added to image_name) and
`--image-type venv` inside a notebook "just works" without any fiddling

llama_stack/distribution/utils/exec.py

@@ -22,6 +22,19 @@ def run_with_pty(command):
         return _run_with_pty_unix(command)
 
 
+def in_notebook():
+    try:
+        from IPython import get_ipython
+
+        if "IPKernelApp" not in get_ipython().config:  # pragma: no cover
+            return False
+    except ImportError:
+        return False
+    except AttributeError:
+        return False
+    return True
+
+
 # run a command in a pseudo-terminal, with interrupt handling,
 # useful when you want to run interactive things
 def _run_with_pty_unix(command):