chore: prep for Hugo site

Description

This MR prepares the CI docs for the Hugo site. It makes the following changes:

• Adds a CI job to test CLI docs on merge requests to check that they will work with Hugo.
• Locates and formats images according to the docs style guide

Related Issues

#219

How has this been tested?

To test, we've run the hugo job against a branch of the docs repo that has be updated to pull in the CLI docs. You can see the output here: https://docs.gitlab.com/review-mr-1404/cli/

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap