Add Progress Bar instead of Loading component

[MCBoarder289]

I would like to implement a progress bar when retrieving the book data from the multi-page shelfs. A simple percentage of 1 / num_pages would suffice, but it would require some refactoring of the cache, including implementing some kind of a background queue (diskcache for now, but could be Celery with Redis to be more productionized).

Helpful stackoverflow on implementing this: https://stackoverflow.com/a/77109011

[MCBoarder289]

Perhaps a loading component but with modal-like features (making the background darker) would work as a medium term solution? Here's some links that might be useful:

• https://community.plotly.com/t/show-loading-spinner-over-graph/46992/2
• https://community.plotly.com/t/setting-type-and-color-for-dcc-loading-using-css/65030/2
• Closing Behaviors of dbc.Modal - maybe we can trigger the input with the loading state?

[MCBoarder289]

Another helpful link with background callbacks: https://stackoverflow.com/a/77024903

[MCBoarder289]

Actual render implementation on this: https://community.plotly.com/t/dash-background-callbacks-on-render-how-to-set-up-celery-background-workers/77199

[MCBoarder289]

Not sure this is needed now that the goodreads parser is much faster, and we've eliminated the isbn fallback query.

Happy to reopen later if we think this is still needed.