new icon: mamba (original)

[sghng]

Double check these details before you open a PR

• [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 at the correct alphabetic position as seen here

Closes #2554

See: https://github.com/mamba-org/mamba/blob/main/docs/source/_static/logo.png

Mamba is an alternative for the conda package manager.