Water heater gas control valves are simple devices without simple means to retrofit electronic ignitions. A knowledgeable controls technician will be able to do it, but will not do it for liability reasons. This means it can be done on one’s own with much effort, more than normal expense, and dangerous possibilities. Thus the water heater manufacturer and code officials will give no warrantee and you will void your insurance approvals.
It is simpler and less expensive to buy a water heater with the capability built in from the factory.