Only send recording snapshots if there was en error (eg $exception)

[marandaneto]

Description

https://posthog.slack.com/archives/C09LZA7FBEZ/p1769727378061099

today we send snapshots if session replay is enabled
there could be a mode where we keep recordings in memory until an error happens, and discard after a while if nothing is broken

[marandaneto]

@PostHog/team-replay this would be useful on the JS SDK as well
important note here: the recording should be happening before the error event, so trigger by events wouldnt work in this case

[pauldambra]

we do this in JS SDK with an event trigger
when the JS SDK is waiting for an event trigger we keep a short buffer of up to 1 minute so that we can start the recording from before the trigger event

[pauldambra]

(we could package this more nicely in the UI)