[FEATURE REQUEST] Dark-mode compatible SVGs.

### Problem

A few users wanted dark-mode compatible versions of SVGs currently in the repo (ex. see #973).

### Suggested feature

We could allow dark-mode compatible SVGs to be added to the repo. Before, we weren't accepting them since it'll clutter the repo. If the user wants dark-mode, they can just download the SVGs and edit it to their taste. However, more and more people are now using dark-mode. Perhaps we should accommodate these needs from the community and change our policy.

### Why should we have this feature?

_No response_

### Additional information

This would require:
- A new naming scheme for dark-mode compatible SVGs. I'm thinking it's something optional, like `wordmark`. So say an SVG can be named `express-original-dark.svg` or something similar.
- Updates to the docs about this new type of icons
- Updates to the websites and script checking to accommodate this new icon type.