Memory leak in ApnsChannelPool

[Sycamore-M]

Hi，

We have an offline push service. After running for a few months, an out of memory issue occurred.

By analyzing memory snapshots, it was found that there are hundreds of thousands of DefaultPromise stacked in ApnsChannelPool.pendingAcquisitionPromises

We had to restart the service regularly before this issue was fixed.

pushy:0.15.4
jdk:11.0.25
netty:4.1.101.Final

[Sycamore-M]

I have found that when the SSL certificate expires, ApnsChannelPool.pendingAcquisionPromises will continue to expand.