Capture request/response bodies for audit-log via pre/post-function

Body capture lives in dedicated audit-log-body-capture(-bindings).yaml
files, separate from audit-log.yaml itself, so they can be dropped
without touching the base logging plugin (degrades gracefully to
metadata-only via nil custom_fields). Response body captured in
body_filter (chunk-accumulated) rather than the log phase, which
cannot call kong.response.get_raw_body() directly.

kong/mcp/audit-log.yaml

@@ -5,8 +5,13 @@ metadata:
   namespace: ${NAMESPACE}
 plugin: http-log
 # dev only: the raw Authorization (JWT) header is captured in clear text,
-# not acceptable as-is for a non-dev environment.
+# not acceptable as-is for a non-dev environment. request_body/response_body
+# below read from kong.ctx.shared, populated by audit-log-body-capture.yaml
+# — nil (and silently omitted) if that file isn't applied.
 config:
   http_endpoint: ${AUDIT_LOG_ENDPOINT}
   method: POST
   content_type: application/json
+  custom_fields_by_lua:
+    request_body: "return kong.ctx.shared.audit_request_body"
+    response_body: "return kong.ctx.shared.audit_response_body"