Automate Gallery Example Structure

[juanitorduz]

Follow up of #1611

We can use the same strategy as in pymc-devs/pytensor#1150 to automate the galley structure as

HEAD = """
Example Gallery
===============
.. toctree::
   :hidden:
"""

SECTION_TEMPLATE = """
.. _{section_id}:
{section_title}
{underlines}
.. grid:: 1 2 3 3
   :gutter: 4
"""

ITEM_TEMPLATE = """
   .. grid-item-card:: :doc:`{doc_name}`
      :img-top: {image}
      :link: {doc_reference}
      :link-type: {link_type}
      :shadow: none
"""

folder_title_map = {
    "introduction": "Introduction",
    "rewrites": "Graph Rewriting",
    "scan": "Looping in Pytensor",
}

We did not do it in #1611 because we wanted to have more freedom to specify the layout, comments and custom notebook titles and descriptions. Still, we might want to automate it as much as possible.

[williambdean]

Maybe we use this template and some yaml? Or tagging the notebook itself?