Hopefully someone with better knowledge in this area will offer more info or other suggestions but this is what I found on Wowpedia that sounds promising.
https://wow.gamepedia.com/Events#C_InstanceEncounter
As to sending to a remote server after the instance, you would have to log out of the game and have another app read in the saved variables written to by the addon and send it to the remote server as required.
If you want to do this per boss rather than encounter, you would have to log out and back in after the transfer of data etc and I am not sure how that would affect the event monitoring with you joining and stopping the group after entering the instance etc.