fix(subscriptions): Don't rely on aggregate names in subscription processor. (#18775)
fix(subscriptions): Don't rely on aggregate names in subscription processor. (#18775)

This fixes an issue where the aggregate name unintentionally changed and it broke the subscription
consumer.

I originally implemented this code to use the name explicitly, in case we start receiving mulitple
values at some point. I don't see any reason that this will be happening any time soon, so just
assuming a single value and grabbing it instead. This should be less brittle when we're migrating
data.

Fixes SENTRY-GCR
beeftornado/sentry,beeftornado/sentry,beeftornado/sentry