Transition to new carpentries format

[dc2917]

Bulk transition

• Update the course site to use the new Carpentries Workbench format

Further refine

• In the learners/setup.md file use :::::::::::::::: spoiler fenced div to get properly aligned drop downs
• Properly align bullets in the spoiler above
• For figures use the correct format: ![optional caption that appears below the figure](figure url){alt='alt text for accessibility purposes'}
• Correct the code fences: Replace ```commands, sh or ```commands with ```bash​
• Include a docker-compose.yml
• Provide descriptive alt text where necessary (Refer: Provide descriptive alt text for images rse_further_git_course#128)
• Use Imperial branding: logo, colours (Refer: Use Imperial branding rse_further_git_course#131)
• Effect of light/dark toggle on images (Refer: Light/dark toggle effects images rse_further_git_course#132)
• The README, authors/contributors, contributing guidelines might need an update (Refer: Missing links in README rse_further_git_course#140, Tailor contributing guidelines rse_further_git_course#141)
• Post transition recommended steps. Also Carpentries are rolling out new versions of GA, so make sure the repo is updated as well)