Add copy-to-clipboard button for code snippets

[SnehaChaursia]

Description of Changes

This PR introduces a highly requested quality-of-life feature for the documentation website: a "Copy to Clipboard" button for all code blocks.
Changes made:

• Code Injection (js/copy-code.js): Added a vanilla JavaScript file that dynamically injects a <button> into all .highlighter-rouge elements.
• Clipboard API: Utilizes the modern navigator.clipboard.writeText API to securely copy code text, with a robust fallback for older browsers or non-secure contexts.
• Styling (css/customstyles-precice.css): Styled the button to sit unobtrusively in the top right corner of code snippets. The button remains transparent and elegantly fades in on hover.
• Global Integration (_includes/footer.html): Included the new JavaScript file in the global footer so it functions seamlessly across all documentation pages and tutorials.
• Visual Feedback: The button temporarily changes to read "Copied!" with a checkmark upon successful click.

Verification

• Tested locally using bundle exec jekyll serve.
• Verified the button correctly targets all code blocks without capturing unintended HTML structure.
• Verified visual feedback timeout works as expected.

ScreenShot

[SnehaChaursia]

@MakisH Please take a look on this feature.

[MakisH]

I am aware of this PR (and many other new PRs), I will take a look later in a few days. Busy week coming up.