docs: add copy to clip for code snippets

[wgwz]

Description

This should add the ability for the code snippets in the documentation to have a copy to clipboard feature.
I tried testing locally but encountered some errors after doing a fresh clone, and cd-ing to docs and running yarn && yarn dev.
It was a bunch of messages like this:

sed: 1: "commands/regen_version.md": command c expects \ followed by text   

But it does seem to be working in deploy preview!
https://deploy-preview-1981--regen-ledger-docs.netlify.app/

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Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[ryanchristo]

LGTM. The sed errors are likely due to you being on a mac. Nothing to worry about.