Add upstream mono color kotlin icon

Purpose

Add an upstream kotlin icon. With our migration of the file icons into this repo, unfortunately we lost: gitlab!76988 (merged)

Side-Note: Even though we are currently choosing the #7F52FF colored-icon, we lose the colors somewhere in our minification process. I verified that this isn't the case in newer versions of svgo / svg spriter. So once we update those, we get the color back.

Screenshots

Before	After
https://gitlab-org.gitlab.io/gitlab-svgs/file_icons?q=kotlin&size=image-hu	http://leipert-add-mono-color-kotlin-icon.34.140.25.101.nip.io/gitlab-svgs/file_icons/?q=kotlin&size=image-hu

Checklist

For a new icon and/or illustration:

• Link to related design issue:
• If this adds an icon ensure that it follows the new icon checklists.
• If this adds an illustration ensure that it follows the new illustration checklists.

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.