Reduce pgBackRest retention to 14 days

[kmandryk]

Update both PostgresCluster base manifests to expire pgBackRest full backups after 14 days, and document the new retention policy in the environment and instance template docs.

Summary

Backup PVCs were running out of space in production. In effect, only approximately 17 days worth of backups could be held at the current size of the application database backup PVC. This change alters the retention policy to be 14 days; the platforms team also retains offsite backups with a retention period of 90 days, so a 30 day retention policy is not really necessary.

In addition to these code changes, a request has been made to expand storage in the production namespace so we can also expand the PVC for the application backups.

Changes

Testing

Checklist

By submitting this pull request, I acknowledge that I have attempted to meet the following:

• a self-review of my code
• commented code particularly in hard-to-understand areas
• corresponding changes to the documentation where required
• changes tested to the best of my ability
• no new errors or non-functional code