pg-upgrade-logical: Code improvement (tasks from the TODO list)

This MR adds tasks and code improvements from TODO list

What's new

• upgrade.yml: Add missing tags for preparatory tasks
• pre_checks: Update task "Stop Chef client" (use "chef-client-disable" command)
• pre_checks: Add task "(TARGET) [Disable DB Cron Daemon] Stop cron service"
• pre_checks: Add task "Drop table test_replication if exists"
• pre_checks: Check the current version of pg_repack (if installed)
• initdb: clean the pg_new_datadir directory before initdb (to exclude the presence of a directory from previous tests)
• initdb: Specify "install user" for initdb command (fix for !406 (comment 1369085630))
• Add pg_hba rule "local all gitlab-psql trust" before pg_upgrade
• Comment out "restore_command" before start Postgres after the upgrade
• Fix /tmp/... file permissions (add the date to the file name)
• Add tasks to delete subscriptions and publications/slots after the upgrade and switchover
  • Stop logical replication only if the leader traffic is switched
• Update README
• Move tasks "Stop Chef client and cron" to stop_services.yml

TODO

• Perform a test in a benchmarking environment