new icon: zsh (original, original-wordmark, plain, plain-wordmark, line, line-wordmark)

[canaleal]

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• [x] PR does not match another non-stale PR currently opened
• [x] PR name matches the format new icon: Icon name (versions separated by comma). More details here
• [x] PR's base is the develop branch.
• [x] Your icons are inside a folder as seen here
• [x] SVG matches the standards laid out here
• [x] A new object is added in the devicon.json file as seen here

This PR closes #1717

Link to prove your SVG is correct and up-to-date.

• ZSH Website
• ZSH Github Official Branding

ZSH uses and orange and black color scheme for the original SVGs. As per the ZSH official branding guide, black should be used for a flat plain icon instead of orange.

The logo with the ZSH is the original, whereas the logo with ZSHELL is the wordmark as shown in the guide.