[Feature] Server image: map server.urls_to_pd and server.deploy_in_k8s from the environment, and stop editing conf files in place #3286

Feature Description (功能描述)

The Server image entrypoint maps a set of environment variables onto the conf files (docker-entrypoint.sh:161-172), but two keys a Server on PD needs in Kubernetes have no mapping:

• server.urls_to_pd: the URL the Server registers with PD
• server.deploy_in_k8s

The Helm chart therefore wraps the entrypoint and rewrites rest-server.properties itself before execing it (server-deployment.yaml:161-232).

The entrypoint also edits the conf files in place: set_prop_encoded runs sed -ri on the file under conf/ (docker-entrypoint.sh:65-66). The image's conf/ must be writable, so the chart refuses readOnlyRootFilesystem for Server (_helpers.tpl:838-839).

Proposal:

1. Map HG_SERVER_URLS_TO_PD to server.urls_to_pd and HG_SERVER_DEPLOY_IN_K8S to server.deploy_in_k8s, next to the existing HG_SERVER_* mappings.
2. Render the effective conf into a writable directory (a copy of conf/ under a data or temp path) and start the Server from it. The image's own conf/ is then never modified, and readOnlyRootFilesystem becomes possible once [Feature] Run the PD, Store and Server images as a non-root user #3211 (non-root image) also lands. feat(dist): Make conf/logs/plugins/pid paths overridable and fix log4j2 config resolution  #3253 makes the conf path overridable, which this step could build on.

With both, the chart can drop its wrapper. The TODO at docker-entrypoint.sh:156 (from #3260) points here.

Not proposed for 1.8.0: the chart's wrapper covers it.