Expand Collapse SubGraphs in a Mermaid flowchart

[ameydesh]

Hi there,

First, I want to express how much I love the rendering capabilities and the simplicity of use with Mermaid diagrams – it's truly fantastic!

That said, I've noticed that there's currently no built-in feature for expanding or collapsing subgraphs, which could be a real game-changer for large, complex flowcharts with many subgraphs or nested subgraphs.

The ability to collapse/expand subgraphs would greatly improve the user experience, especially when working with intricate diagrams. Ideally, when a user clicks on a subgraph, it should toggle between a collapsed and expanded state. When collapsed, the subgraph would condense into a single node, and when expanded, the subgraph would reveal all the nodes and edges it contains.

Would it be possible to add such a feature to Mermaid? I believe it would be incredibly helpful for users managing more complex diagrams.

Looking forward to hearing your thoughts on this!

@knsv , @sidharthv96

Thanks,
Amey