[data grid] Remove GridEvents enum

[flaviendelangle]

I v6, I propose we drop the GridEvents enum in favor of a simple type generated from the keys of GridEventLookup (the actual GridEventsStr.

That way, we will not have to define the pro-only and premium-only events inside the gridEvents.ts file which is located in the community package.
Just like for pre-processor, there is no reference to pro-only processors inside the community package because they are based on the lookup which is augmented in the pro and premium packages.

-apiRef.current.subscribeEvent(GridEvents.rowGroupingModelChange, handleRowGroupingModelChange)
+apiRef.current.subscribeEvent('rowGroupingModelChange', handleRowGroupingModelChange)

-apiRef.current.publishEvent(GridEvents.rowExpansionChange)
+apiRef.current.publishEvent('rowExpansionChange')

-useGridApiEventHandler(GridEvents.rowGroupingModelChange, handleRowGroupingModelChange)
+useGridApiEventHandler('rowGroupingModelChange', handleRowGroupingModelChange)

Goals

• Do not leak pro-only and premium-only code on the community package
• Needed to allow user to create there own plugins with there own events

Work to do

• V5: Stop using GridEvents in our codebase and docs (replace with the string which is already supported)
• V5: Mark GridEvents as deprecated (I don't see how we could do a runtime warning)
• V5 : Move the comments from GridEvents to GridEventLookup and update buildGridEventsDocumentation
• V6: Remove GridEvents