Fixes https://emqx.atlassian.net/browse/EMQX-9603
Rather than relying on a JWT worker to produce and refresh tokens, we
could just produce then on demand when pushing the messages to GCP
PubSub. That can generate a bit of extra work (as multiple processes
might realize it’s time to refresh the JWT and do so), but that
shouldn’t be much. In return, we avoid any possibility of not having
a fresh JWT when pushing messages.
Thales Macedo Garitezi