[Features] RSM Heterogeneous Pods Supports

[free6om]

Currently all pods in a component share the same podTemplate and volumeClaimTemplate, and restricted by the current design(one RSM mapping to one StatefulSet), it's impossible to remove pod with ordinal less than the biggest one. but there are scenarios need to break these constraints:

1. in a primary-secondary cluster, the secondary pod should be configured with less CPU or memory resources for cost saving.
2. in a raft-based cluster, the logger pod should be configured with less storage resource for cost saving.
3. some outer system that interacting with KubeBlocks has its own update strategy and needs the capability to apply it to the low-level pod directly.

A reasonable design to overcome these drawbacks is mapping RSM's one replica to one StatefulSet, and provides API field(s) in RSM, Component and Cluster to configure each replica separately.
Another design is managing pods and pvcs directly to allow separate configuration.

[Somiacao]

scenario：

1. implement of scale down specified instance
2. specify nodes list to create pods

[github-actions]

This issue has been marked as stale because it has been open for 30 days with no activity

[free6om]

the stateful part is not finished yet.