update_pgcluster.yml: Wait for caches to warm up after reboot

[vitabaks]

Wait N minutes for the caches to warm up after restarting the server before updating the next server.
Note: Applicable when there are multiple replicas.

Variable: reboot_host_post_delay, default value: 5 (minutes).

• Note: The required value of the variable depends on the size of the database, the load, and so on. But in most cases, it is better to raise the value to give more time to warm up the cache. If replicas are not used to balance the reading load, then delay can be disabled (value 0).

Additionally

• All variables have been moved from the update_pgcluster.yml playbook file to update role vars/main.yml
• Add more variables: reboot_host_after_update, reboot_host_timeout
• Specify the full path to the psql command