3D array: choose obs and var, show 3rd dimension as lineplot/scatterplot

[eroell]

User story
For a 3D array in anndata we are working with (shape n_obs x n_var x n_repeats_of_measurement), it would be very interesting to visualize the data along this third axis.

Preferred solution
Currently, a user can select a gene, and have e.g. violin plots shown for this gene. In analogy, I could imagine here to first

1. select a gene
2. select an observation

(So at this stage having selected a 1 x n_repeates_of_measurements vector.)

Then, display a scatterplot or lineplot of this vector. The values in this vector on the y-axis, and maybe just integers of the range from 1 to n_repeates_of_measurements on the x-axis?

Possible alternatives

• Allow to choose multiple genes, observations
• Allow for the x-axis labels to be altered rather than just the range

Opening the issue over a discussion with @ilan-gold.
For 3D things anndata, I link this issue here: scverse/anndata#244