feat: Add rust-ferris-light and rust-ferris-dark themes

[ankddev]

Description

Add both light and dark variants of themes with Rust's language mascot's colors.

Type of change

• New feature (added a non-breaking change which adds functionality)
• Updated documentation (updated the readme, templates, or other repo files)

How Has This Been Tested?

• Tested locally with a valid username
• Tested locally with an invalid username

Checklist:

• I have checked to make sure no other pull requests are open for this issue
• The code is properly formatted and is consistent with the existing code style
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Screenshots

Light

Dark

[DenverCoder1]

Thanks again for the contribution!