support vertical pod autoscaler

[hawkingrei]

Enhancement

Vertical Pod Autoscaler (VPA) frees users from the necessity of setting up-to-date resource limits and requests for the containers in their pods. When configured, it will set the requests automatically based on usage and thus allow proper scheduling onto nodes so that appropriate resource amount is available for each pod. It will also maintain ratios between limits and requests that were specified in initial containers configuration.

If TiDB supports vertical pod autoscaler, we changed machine configuration such as CPU Core or Max memory. we don't restart tidb to create a new tidb to enable this configuration.

• support cgroup v1/v2 to get cpu/memory limit

• util: improve cgroup to support Vertical Pod Autoscaler  #36901