Expand-All/Collapse-All/groupDefaultExpanded support with SSRM

You can expand row groups by default on load when using SSRM using a callback as documented here:
https://www.ag-grid.com/javascript-data-grid/server-side-model-grouping/#open-by-default

Calling api.expandAll() and api.collaseAll()  methods has no effect when using SSRM because not all rows are loaded.

You can only expand/collapse group nodes which are already loaded using api.forEachNode and calling the setExpanded method on each group node.

https://www.ag-grid.com/javascript-data-grid/grid-api/#reference-rowNodes-forEachNode

https://www.ag-grid.com/javascript-data-grid/row-object/#reference-expand-setExpanded

However, this will only affect rows which are already loaded by the grid.