Improve course card images

[ryan-storey]

Whilst our current course card images are suitable and visually appealing to users, they are all exactly the same. As we will have 25 courses (and counting!), this means that there will be 25+ courses with exactly the same image, and there will be no way to differentiate except by the title below the project.

Creating a custom image for every guide would be quite 'expensive'.
Perhaps it would be a good idea to alter the course card so that they are different for each guide, such as using an Open Liberty template with a subtitle that we can change for each guide, that contains a tagline such as "MicroProfile Health", "Deploying to OpenShift", depending on the course content.