Add mermaid graph output for duplicates

[Jake-Shadle]

Currently we create a dotviz graphs when duplicates are detected and the user sets a graph output directory, which than then be fed through eg dot to generate a png etc to display to a user. However, now that Github has direct support for mermaid JS, it makes sense to add this as an additional option, probably via Flowcharts. Ideally this would allow users to show the duplicate diagram in github actions, though I don't know if that is actually supported or not.