feat(helm): add HTTPRoute filters, celeryConfig, remove example provider

[lewisjared]

Summary

• Add filters support to API and Flower HTTPRoute templates, enabling Traefik middleware integration (e.g. ForwardAuth for Authelia)
• Add flower.celeryConfig rendered as a ConfigMap (celeryconfig.py) with CELERY_CONFIG_MODULE/PYTHONPATH env vars and volume mount, matching the upstream ref chart's behavior for pickle content deserialization
• Add configmap checksum annotation to Flower deployment for automatic pod restart on config change
• Remove example provider from default values

Context

These changes align the climate-ref-aft chart with features present in the upstream climate-ref chart (ref) that are needed for production deployments:

• HTTPRoute filters are required for Traefik Gateway API deployments that use ForwardAuth middleware (e.g. Authelia authentication)
• celeryConfig is needed so Flower can deserialize pickle-encoded task results from workers that set CELERY_ACCEPT_CONTENT: '["json", "pickle"]'
• example provider is not needed in production and wastes a pod

Test plan

• helm template renders correctly with filters enabled
• helm template renders flower ConfigMap with celeryconfig.py
• helm template no longer renders example provider resources
• Existing deployments without filters/celeryConfig overrides continue to work (defaults are empty list / existing accept_content)

[lewisjared]

Climate-REF/climate-ref#550