outdated template notebooks hardcode wrong notebook_image_uri

[OwenPriceSkelly]

Noticed when notebook start-ing a notebook that didn't already exist that the first cell looks like

# This cell is auto-generated by Garden. Don't delete it. Do keep it as the first cell.
# It records the base image and requirements you passed to `garden-ai notebook start`.
# That way the next time you run this notebook Garden can start it with the same libraries.

notebook_image_uri = "gardenai/base:python-3.9-jupyter"
notebook_requirements = None

even though a) I asked for (and was correctly running in) a base image with 3.10 and b) the new generated cell contents are expected to be formatted like this:

"""
NOTEBOOK_METADATA = {
  "NOTEBOOK_BASE_IMAGE_NAME": "3.10-base",
  "NOTEBOOK_REQUIREMENTS": null
}
"""

I think this is just a matter of updating the template and handling the edge case where the notebook doesn't yet exist better

Assumptions:

1. 2.

Acceptance Criteria

Given..., when..., then...