Make cache replication in Jira Data Center always asynchronous

Problem Definition

The cache replication in Jira Data Center 7.9 and later is asynchronous by default, which means that cache modifications aren’t replicated to other nodes immediately after they occur, but are instead added to local queues. They are then replicated in the background based on their order in the queue.
There is an option to "disable the asynchronous cache replication", and enables the synchronous one instead (used in Jira 7.8 and earlier) which can be used as a fallback scenario.

See related docs: https://confluence.atlassian.com/enterprise/jira-data-center-cache-replication-954262828.html

Taking into account that option was rarely used and it complicates the code (see JRASERVER-71160), removing the synchronous code will be beneficial.

Suggested Solution

Remove support for synchronous cache replication (make cache replication in Jira Data Center always asynchronous).

Workaround

None