docs: Add example of blueprint using pg_backup_start/pg_backup_stop

[hairyhum]

Change Overview

pg_backup_start and pg_backup_stop require session to be active while files are copied.

This example blueprint allows doing that by:

• Creating a pod to run for a duration of a backup with psql session in there: createBackupPod phase
• Sending pg_backup_start command to the running psql session: startBackup phase
• Copying the files: copyFiles phase
• Sending pg_backup_stop command to the running psql session: stopBackup phase
• Cleaning up the session pod in deferPhase

Pull request type

Please check the type of change your PR introduces:

• 🚧 Work in Progress
• 🌈 Refactoring (no functional changes, no api changes)
• 🐹 Trivial/Minor
• 🐛 Bugfix
• 🌻 Feature
• 🗺️ Documentation
• 🤖 Test
• 🏗️ Build

Issues

• fixes #issue-number

Test Plan

• 💪 Manual
• ⚡ Unit test
• 💚 E2E

[mlavi]

Thank you!