documentation: add copy as markdown button

[sona-gem]

Closes #1334

Description of changes:
Added a "Copy as Markdown" button to Amazon Braket documentation pages.

The button converts documentation content into Markdown, including headings,
links, emphasis, lists, inline code, and code blocks and copies the result
to the clipboard.

Testing done:

• Ran node --check .\doc\_static\copy-markdown.js
• Ran git diff --check
• Successfully built the documentation with Sphinx
• Manually tested the "Copy as Markdown" button on the generated documentation
• Verified headings, links, lists, inline code, emphasis, and code blocks
  are copied as Markdown

Merge Checklist

General

• I have read the CONTRIBUTING doc
• I used the PR title format described in CONTRIBUTING

[rmshaffer]

@sona-gem thank you for the suggested contribution!

After we looked into this a little more, it turns out that ReadTheDocs already has an agent-friendly solution here. See: https://docs.readthedocs.com/platform/stable/reference/markdown-for-agents.html

tl;dr: ask the agent to use Accept: text/markdown in the requests for the docs pages, and it will come in markdown format automatically. This feature is enabled automatically on all documentation domains hosted on Read the Docs, with no configuration required. So this should work today on https://amazon-braket-sdk-python.readthedocs.io/en/stable/ and the docs sites for our other repos.

As a result, we won't want to add the button to the pages directly. So I'm closing this PR (and the linked issue) as not planned.