Feature: PCA aggregation for n >= 4 channels in render_images

[timtreis]

[LucaMarconato]

I am experiencing problems related to n >= 4 channels: this is the Xenium notebook in the docs

And this is from the current main:

Before I think the image was treated as RGBA, now the INFO says Your image has 4 channels. Sampling categorical colors and using multichannel strategy 'stack' to render..

RGBA may have not been the best approach in the first place. What's your recommended change to the code? Shall I pass a custom palette?

[LucaMarconato]

I changed the code in the notebook: now I plot single-channels.