resource-manager: add billing RU metric by keyspace RU version #10481
Description
Enhancement Task
Add a Prometheus-only billing RU metric in resource manager.
The metric should:
- expose billing RU totals without sending them to metering
- switch the billing formula dynamically by each keyspace's
ru_version - use
RRU + WRU + SQL RUfor v1 keyspaces - use
TiKV RU v2 + TiDB RU v2 + TiFlash RU v2for v2 keyspaces - follow the existing RU v1/v2 metric naming and collection flow