Regression in demo site

[mattgallagher92]

As we've seen with other apps when upgrading to AG Grid v31, the demo site's column states are lost when changes are made. For example, editing the name of an athlete resets all the column widths.

Fix this by making the column defs part of the component's state.

[isaacabraham]

@mattgallagher92 is there a guide / sample for doing this - that could then make this an "up-for-grabs" kind of issue.

[mattgallagher92]

Not in F#, but it basically comes down to the recommendations in https://www.ag-grid.com/react-data-grid/react-hooks/

In particular, we've seen problems relating to https://www.ag-grid.com/react-data-grid/react-hooks/#column-definitions