Add fade options for promt heads and tails

Description

This adds the configuration options for using fade for prompt heads and tails.

Motivation and Context

powerlevel10k has a fade option which I really like, but my primary shell is fish.

Screenshots (if appropriate)

Tail:

Head:

How Has This Been Tested

1. Created a fork of tide
2. Cloned fork locally
3. Uninstalled tide with fisher fisher remove fisher remove ilancosman/tide@v6
4. Installed local tide clone with fisher install .
5. Went through tide configure

• [x] I have tested using Linux.
• [x] I have tested using MacOS.

Checklist

• [x] I am ready to update the wiki accordingly.
• [ ] I have updated the tests accordingly.