Fix #1544: Restore Bitnami Helm dependency images

[theonlypal]

Description

This PR closes #1544 by pointing the pinned Bitnami Redis and PostgreSQL subcharts at the immutable images Bitnami moved from docker.io/bitnami to docker.io/bitnamilegacy.

The chart currently resolves versioned Redis, PostgreSQL, and helper-image tags that no longer exist in Bitnami's primary Docker Hub repositories. A default installation therefore fails while pulling its dependencies unless users rewrite every rendered image with a Helm post-renderer.

This keeps the dependency versions already selected and tested by the chart, restores pullable images without an installation-time rewrite, and avoids silently upgrading Redis or PostgreSQL across major versions.

Changes

• Point the gateway Redis deployment at the matching legacy Redis image.
• Point the JuiceFS Redis deployment at the same matching legacy image.
• Point PostgreSQL and its volume-permissions helper at their matching legacy images.
• Cover the optional Redis Sentinel, metrics, volume-permissions, and sysctl images.
• Cover the optional PostgreSQL metrics image.
• Preserve all existing Helm dependency and application versions.

Verification

• helm dependency build passes.
• helm lint passes.
• The default chart renders successfully.
• Metrics, volume-permissions, and sysctl configurations render successfully.
• Redis Sentinel configurations render successfully.
• No tested configuration renders a docker.io/bitnami/* dependency image.
• All seven rendered docker.io/bitnamilegacy/* tags resolve through the Docker registry.
• Helm chart packaging passes.
• The complete Go package test suite passes.
• The Python SDK suite passes with 201 tests passed and 2 integration tests skipped.
• The branch is conflict-free with current main.

Closes #1544

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Summary by cubic

Restores pullable Bitnami Helm dependency images by switching Redis and PostgreSQL subcharts to immutable tags under docker.io/bitnamilegacy, fixing default install failures without upgrading across major versions. Closes #1544.

• Bug Fixes
  • Redirect Redis (gateway and juicefs-redis) to bitnamilegacy/redis and supporting images (redis-sentinel, redis-exporter, os-shell, sysctl).
  • Redirect PostgreSQL and helpers to bitnamilegacy/postgresql, os-shell, and postgres-exporter.
  • Preserve all existing chart and dependency versions; only the image repository path changes.

^{Written for commit f381f33. Summary will update on new commits.}