Visualization: Custom Image Heatmaps

**Is your feature request related to a problem? Please describe.**
I find it challenging to visualize data on custom images, like mechanical parts. Metabase supports heatmaps with real-life maps using latitude and longitude, but there is no option to overlay heatmaps on custom images, which limits the ability to represent data in a context-specific manner for many applications.

**Describe the solution you'd like**
I would like Metabase to support creating heatmaps over custom images. This feature should allow users to upload custom images, place a grid overlay on these images, and map data points to specific grid cells.

**Describe alternatives you've considered**
An alternative would be to use external tools to create heatmaps on custom images. Unfortunately, you can't import these into Metabase, resulting in the need to check two different sites, which is inefficient and inconvenient.

**How important is this feature to you?**
This feature is very important as it would significantly enhance the ability to visualize and analyze data in context-specific scenarios.

**Additional context**
Below is an example image illustrating the desired functionality. In this example, a mechanical part is shown with specific areas highlighted using a heatmap. This feature would allow users to directly visualize problem areas on the part image.


⬇️ Please click the 👍 reaction instead of leaving a `+1` or `update?` comment

No implementation files, tests, or entry points are identified in the issue. Start by reviewing the requested custom-image upload, grid overlay, and data-point mapping requirements, then clarify the supported image and heatmap behavior; done should mean users can create and view a heatmap over a custom image in Metabase.

Written by the indexing model from the issue text.