Add configuration to mindmaps

[lettuceDestroyer]

I think it would be nice if there was a way to configure the behaviour of the mindmap similar to how the flowchart has a configuration. The following configuration options came to mind:

• change default shape of mindmap: While the mindmap does have a default shape, I thinkt it would be nice if all shapes could be changed based on a configuration
• colours of nodes: it would also be nice if we could pass colours as hex, which will be used by the mindmap to colour nodes (see discussion #5171)
• change "links-between-nodes": The current links between nodes are rather thick and not nice to look at. It would be nice if we could choose one type of link, similar to how we got the option for flowcharts
• layout: There should be the option to change the layout of the mindmap, as a mindmap can be quite hard to read when spaced out. This could be achieved by using the same reder-mechanism as a flowchart (see discussion #4850)

I'd be willing to try something myself but for that I'd need someone to point out how to add configurations to diagrams 😅.