Decouple write lock and read lock of PQ

Currently, every [write](https://github.com/elastic/logstash/blob/8.13/logstash-core/src/main/java/org/logstash/ackedqueue/Queue.java#L420) and read [action](https://github.com/elastic/logstash/blob/8.13/logstash-core/src/main/java/org/logstash/ackedqueue/Queue.java#L617) shares the same lock. Write action always write to the head page, while the read action could read from the tail or head page depending on the workers speed.

In case of reading the tail page, read action no need to wait the write side to release the lock to do read. Head page and tail page do not share anything and can work parallel.

Start in logstash-core/src/main/java/org/logstash/ackedqueue/Queue.java at the write action around line 420 and read action around line 617, and trace which page state each operation accesses. The work is done when reads from the tail page no longer wait for writes to the head page, while shared state remains safely synchronized.

Written by the indexing model from the issue text.