Add ROS topic to track Grab start, bin name, bin saved messages

[mbrosnahan]

We need a topic that can be used to filter ROS bag data for beginning and end of bins so that [we can create] class_score files [for the IFCB dashboard] from ROSbag data.

[rgov]

I think this would belong in the ifcb node. We'd basically add another handler, as @figuernd has already done. We would need to define the message schema but it can probably be very simple, maybe even using built-in message types. Note that these are without timestamps.

[rgov]

Also as a reminder the ROS bag already stores all messages from IFCBacquire so we can already filter for these. It's not very nice in Foxglove Studio because the messages are just given as a list of byte values (as integers) but in code it's easy to scan for them.