This commit resolves the issues with subgraph configuration, specifically for nodeSpacing and rankSpacing. This commit additionally adds an example graph to the `flowchart.html` to demonstrate this resolution. This commit resolves mermaid-js#3258

Removed unnecessary function to pass test coverage CI

Co-authored-by: Nikolay Rozhkov <[email protected]>

There was an issue with overriding the subgraphs with the main graphs direction which this commit fixes. It only overrides `rankdir` on the `setGraph` function so that the subgraph preserves it's `rankdir`. There is likely a better way of doing this by modifying the initialization of subgraph configuration to match the main graph when it comes to other elements in the JSON object which composes the graph label.

As we modify the codebase this added line can be deprecated once we add more modular control to subgraphs such as allowing custom spacing or configurations for them. As `rankdir` is the only thing one can set with the `direction` keyword that is the only variable being overwritten for now.

The code setting the `ranksep` and `nodesep` to subgraphs was made cleaner and more legible while maintaining the intended functionality of subgraph spacing

Co-authored-by: Alois Klink <[email protected]>

This adds E2E testing for spacing and provides more appropriate comments for the changes made to `index.js`