Add custom index page to pn hello apps

[MarcSkovMadsen]

When you run pn hello apps you should be able to go to https://localhost:5006 and see a nice gallery page.

Currently this does not work due to holoviz/panel#3970. When this gets fixed there will be a simple index page.

I would like though a nice gallery page with more info as found at https://www.awesome-panel.org/gallery.

The template can be found here https://github.com/awesome-panel/awesome-panel-extensions/tree/master/awesome_panel_extensions/frameworks/fast/templates/fast_gallery_template

Accept Criteria

• [] The FastGalleryTemplate carved out into its own project awesome-panel-gallery created and managed using the awesome-panel-cli.
  • [] Should support both to be panel served and to be .saved to a standalone html template.
• [] Added to the reference apps at https://github.com/awesome-panel/awesome-panel-cli/tree/main/src/awesome_panel_cli/templates/apps
• [] served automatically by pn hello apps as an index page at /.