PLT-8277 - Add a button to copy to the clipboard a link to the current contract in the Marlowe editor

[palas]

This PR adds a button to the Marlowe Editor that copies to the clipboard a link that will load the current contract in the Marlowe Editor when clicked. The button only works for correct contracts with no holes, since it has to be encoded as JSON.

Pre-submit checklist:

• Branch
  • Tests are provided (if possible)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
  • Relevant tickets are mentioned in commit messages
  • Formatting, materialized Nix files, PNG optimization, etc. are updated
• PR
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested

[paluh]

Thanks a lot!