Ensure Postgres is upgraded in right order for Zero Downtime Upgrades

What does this MR do?

MR fixes issue seen in #294 (closed) where at times an error is thrown when we try to determine Patroni leader on new Postgres boxes during a Zero Downtime Upgrade.

Issue is caused on new boxes as Postgres wasn't being reconfigured until after we run the Patroni leader commands (that need Postgres to be configured).

Fix is to just ensure Postgres is reconfigured first before trying to determine leader. This actually matches the ZDU docs as well (although they have wrong terms as well I'll be addressing separately)/

Related issues

Closes #294 (closed)

Author's checklist

When ready for review, the Author applies the workflowready for review label and mention @gl-quality/get-maintainers:

• Merge request:
  • Corresponding Issue raised and reviewed by the GET maintainers team.
  • Merge Request Title and Description are up to date, accurate, and descriptive
  • MR targeting the appropriate branch
  • MR has a green pipeline
  • MR has no new security alerts in the widget from the Secret Detection and IaC Scan (SAST) jobs.
• Code:
  • Check the area changed works as expected. Consider testing it in different environment sizes (1k,3k,10k,etc.).
  • Documentation created/updated in the same MR.
  • If this MR adds an optional configuration - check that all permutations continue to work.
  • For Terraform changes: setup a previous version environment, then run a terraform plan with your new changes and ensure nothing will be destroyed. If anything will be destroyed and this can't be avoided please add a comment to the current MR.
• Create any follow-up issue(s) to support the new feature across other supported cloud providers or advanced configurations. Create 1 issue for each provider/configuration. Contact the Quality Enablement team if unsure.