feat: implement Flux image update automation for balancer

[TineoC]

This PR implements Flux Image Update Automation for the balancer application.

Depends on: #124
Related to: CodeForPhilly/balancer-main#455

Changes:

1. balancer/kustomization.yaml: Added the Flux automation marker # {"$imagepolicy": "flux-system:balancer"} to the image tag.
2. flux-automation.yaml: Created new Flux resources:
   • ImageRepository: Monitors ghcr.io/codeforphilly/balancer-main/app.
   • ImagePolicy: Configured to automatically pick the latest development build (tags matching .*-dev.[0-9]+). It uses alphabetical sorting to ensure the latest timestamp is chosen.
   • ImageUpdateAutomation: Automatically commits image tag updates back to this repository.

Requirements:

• Flux v2 with Image Reflector and Automation controllers must be installed.
• The cluster must have write access to this repository.

[themightychris]

See notes in #124