Implement copy button

[Kreyren]

Description

Issue transferred from https://codeberg.org/Codeberg/Community/issues/266

On rafined GitHub there is a function that allows to put the file content in a clipbox which i think would be nice here as well

Checklist prior to contribution

• Find the original contributor who created this for refined github

• Found https://github.com/sindresorhus/refined-github/blob/master/source/features/copy-file.tsx

• Git history: https://github.githistory.xyz/sindresorhus/refined-github/blob/master/source/features/copy-file.tsx

• First known commit by @fregante refined-github/refined-github@11b9271

• Concluded that Rafined-github project should be credited for this feature

• Contribution wanted by Gitea