feat: support specified instance scale down

[free6om]

Use Cases

Node Failure

When a physical fault occurs on a specific node, it is necessary to rebuild a replica and subsequently take the affected pod on that node offline.

Data Corruption

When the data of a particular pod is corrupted, it is necessary to rebuild a replica and subsequently take the affected pod offline.

Instance Unavailability

When a pod experiences availability issues such as slow or unresponsive behavior, the best practice is to create a new replica and subsequently take the affected pod offline.

Cluster API

Add the OfflineInstances field to spec.componentSpecs in the Cluster API to describe the instances to be taken offline.

apiVersion: apps.kubeblocks.io/v1alpha1
kind: Cluster
# ...
spec:
  componentSpecs:
  - name: "foo"
    offlineInstances: [ "foo-2", "foo-3"]
# ...

OpsRequest API

Add the offlineInstances field to Ops to override the field in the Cluster.

apiVersion: apps.kubeblocks.io/alpha1
kind: OpsRequest
# ...
spec:
  # ...
  horizontalScaling:
  - componentName: "foo"
    replicas: 2
    offlineInstances:
    - "foo-2"
    - "foo-3"
# ...

Test

Case 1: Specify Instance Offline

Create a 3-instance cluster and use Ops to specify taking the instance with ordinal 1 offline.
Expected result:

1. The Cluster Spec should include OfflineInstances:

apiVersion: apps.kubeblocks.io/v1alpha1
kind: Cluster
# ...
spec:
  componentSpecs:
  - name: "foo"
    offlineInstances: ["foo-1"]
# ...

2. The RSM should actually generate 2 instances with ordinal 0 and 2.

[codecov]

Codecov Report

Attention: Patch coverage is 65.01767% with 99 lines in your changes are missing coverage. Please review.

Project coverage is 65.77%. Comparing base (1b6ef23) to head (1d29e88).
Report is 4 commits behind head on main.

Files	Patch %	Lines
pkg/controller/rsm2/instance_util.go	78.76%	20 Missing and 11 partials ⚠️
pkg/controller/component/rsm_convertor.go	0.00%	29 Missing ⚠️
controllers/apps/operations/horizontal_scaling.go	60.00%	14 Missing and 4 partials ⚠️
pkg/controller/rsm2/reconciler_revision_update.go	56.52%	6 Missing and 4 partials ⚠️
...g/controller/rsm2/reconciler_instance_alignment.go	80.00%	2 Missing and 2 partials ⚠️
pkg/controller/rsm2/reconciler_update.go	50.00%	3 Missing and 1 partial ⚠️
pkg/controller/builder/builder_component.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6958      +/-   ##
==========================================
- Coverage   65.96%   65.77%   -0.19%     
==========================================
  Files         340      340              
  Lines       41356    41391      +35     
==========================================
- Hits        27279    27225      -54     
- Misses      11754    11835      +81     
- Partials     2323     2331       +8     

Flag	Coverage Δ
unittests	65.77% <65.01%> (-0.19%)	⬇️

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[wangyelei]

you add patchStrategy:"merge,retainKeys" patchMergeKey:"name" to verify that template name is the unique key

[free6om]

fixed in: 1d29e88

[free6om]

/cherry-pick release-0.9

[github-actions]

🤖 says: cherry pick action finished successfully 🎉!
See: https://github.com/apecloud/kubeblocks/actions/runs/8595993678