Add optional in-cluster registry proxy for ghcr.io to platform-api chart

[tamalsaha]

What

Adds an optional in-cluster pull-through Docker registry cache to charts/platform-api, gated behind regproxy.enabled (default false). When enabled it runs CNCF Distribution (registry:2) configured as a pull-through cache for the upstream registry (https://ghcr.io by default), so ghcr.io/appscode-charts (and any other ghcr.io) images can be served transparently from within the cluster.

Because the ace umbrella chart embeds platform-api as a subchart, the cache is reachable from ace via platform-api.regproxy.* values.

Routing node/client pulls to the cache (e.g. via containerd registry mirror configuration) is left to the cluster operator — this PR only deploys the cache and its Service.

Changes

• Go API (apis/installer/v1alpha1/ace_platform_api.go): new regproxy field on PlatformApiSpec, backed by Regproxy / RegproxyPersistence types (image, remoteURL, optional username/password, replicas, service, persistence, securityContext, scheduling).
• Templates (charts/platform-api/templates/regproxy/):
  • configmap.yaml — registry config.yml (proxy.remoteurl, filesystem storage, health checks)
  • secret.yaml — upstream credentials, rendered only when username is set
  • deployment.yaml — registry container; config/data/tmp volumes; /v2/ liveness+readiness; auth env injected only when credentials are set; OpenShift-aware securityContext
  • service.yaml — ClusterIP on service.port → container port 5000
  • pvc.yaml — created only when persistence.enabled (otherwise an emptyDir is used)
• Helper (_helpers.tpl): regproxy.registry, resolving ghcr.io/appscode/registry via the chart's registryFQDN + regproxy.image.registry (consistent with the other image helpers).
• values.yaml: new regproxy: block with documented defaults.
• catalog/imagelist.yaml: added ghcr.io/appscode/registry:2.8.3 so the image is mirrored on release.
• Ran make gen — regenerated zz_generated.deepcopy.go, the platform-api values.openapiv3_schema.yaml/README.md, and the ace values.openapiv3_schema.yaml (which now carries the inherited platform-api.regproxy block).

Verification

• go build ./... clean
• helm template renders all five manifests correctly across enabled / anonymous / persistence-disabled paths, and renders nothing when disabled

Notes

• The default ghcr.io/appscode/registry:2.8.3 assumes the release pipeline mirrors upstream registry:2.8.3 (imagelist entry added to drive that). Override regproxy.image.* if needed.
• Uses the registry:2 config layout (/etc/docker/registry/config.yml). Switching to Distribution v3 would require a different config path/schema.