introduce flag --feature-gates to karmadactl register

[zhzhuang-zju]

What type of PR is this?
/kind feature

What this PR does / why we need it:
introduce flag --feature-gates to karmadactl register to describe feature gates for alpha/experimental features of karmada-agent.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

$ karmadactl register -h
Options:

    --feature-gates='':
        Comma-separated list of key=value pairs that describe feature gates for alpha/experimental features
        of karmada-agent. More info: https://github.com/karmada-io/karmada/blob/master/pkg/features/features.go

Does this PR introduce a user-facing change?:

`karmadactl`: introduce flag `--feature-gates` to command `register` to describe feature gates for alpha/experimental features of `karmada-agent`.

[karmada-bot]

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[zhzhuang-zju]

Timeout waiting for file exist /home/runner/.kube/member-tmp-member2.config
https://github.com/karmada-io/karmada/actions/runs/12478154855/job/34825314108?pr=5970#step:5:710

/retest

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Attention: Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Project coverage is 48.22%. Comparing base (c9ca6ac) to head (50be683).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/karmadactl/register/register.go	0.00%	11 Missing ⚠️

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@@            Coverage Diff             @@
##           master    #5970      +/-   ##
==========================================
- Coverage   48.23%   48.22%   -0.02%     
==========================================
  Files         664      664              
  Lines       54749    54760      +11     
==========================================
- Hits        26410    26406       -4     
- Misses      26624    26638      +14     
- Partials     1715     1716       +1     

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[zhzhuang-zju]

/hold for more verification

[zhzhuang-zju]

/hold cancel

[RainbowMango]

/assign

[RainbowMango]

Suggested change

	flags.StringVar(&opts.FeatureGates, "feature-gates", "", ""+
	"A set of key=value pairs that describe feature gates for alpha/experimental features. "+
	"Options are:\n"+strings.Join(features.FeatureGate.KnownFeatures(), "\n"))
	features.FeatureGate.AddFlag(flags)

Can we do that this way, which is the way we did at all the other components, like

karmada/cmd/controller-manager/app/options/options.go

Line 235 in 6144ea5

features.FeatureGate.AddFlag(flags)

[zhzhuang-zju]

I've tried this way, but ran into an issue where I couldn't get the string value of the feature gates when injecting them into the agent's manifest.

[RainbowMango]

why?

[RainbowMango]

It is worth noting that, you don't need to introduce an additional field into CommandRegisterOption anymore.

	FeatureGates string

[zhzhuang-zju]

why?

karmada/vendor/k8s.io/component-base/featuregate/feature_gate.go

Lines 122 to 153 in 7112723

	// MutableFeatureGate parses and stores flag gates for known features from
	// a string like feature1=true,feature2=false,...
	type MutableFeatureGate interface {
	FeatureGate
	// AddFlag adds a flag for setting global feature gates to the specified FlagSet.
	AddFlag(fs *pflag.FlagSet)
	// Close sets closed to true, and prevents subsequent calls to Add
	Close()
	// Set parses and stores flag gates for known features
	// from a string like feature1=true,feature2=false,...
	Set(value string) error
	// SetFromMap stores flag gates for known features from a map[string]bool or returns an error
	SetFromMap(m map[string]bool) error
	// Add adds features to the featureGate.
	Add(features map[Feature]FeatureSpec) error
	// GetAll returns a copy of the map of known feature names to feature specs.
	GetAll() map[Feature]FeatureSpec
	// AddMetrics adds feature enablement metrics
	AddMetrics()
	// OverrideDefault sets a local override for the registered default value of a named
	// feature. If the feature has not been previously registered (e.g. by a call to Add), has a
	// locked default, or if the gate has already registered itself with a FlagSet, a non-nil
	// error is returned.
	//
	// When two or more components consume a common feature, one component can override its
	// default at runtime in order to adopt new defaults before or after the other
	// components. For example, a new feature can be evaluated with a limited blast radius by
	// overriding its default to true for a limited number of components without simultaneously
	// changing its default for all consuming components.
	OverrideDefault(name Feature, override bool) error
	}

features.FeatureGate.AddFlag(flags) has no method to get the string value of the feature gate. Hard to complete fmt.Sprintf(‘--feature-gates=%s’, o.FeatureGates).

[zhzhuang-zju]

I have a question: does it need to verify whether the user-defined featuregate is valid? The method features.FeatureGate.Validate() is used to determine if the user-defined feature gate has been added in [pkg/features/features.go]. This leads to the validation result being highly related to the code at the time karmadactl was compiled. However, karmadactl register should support different versions of karmada-agent.
For example:

• version v1.12 the supported featuregates are: featuregateA and featuregateB,
• version v1.13 the supported featuregates are: featuregateA,

So, using the v1.13 version of karmadactl to execute the register command, setting the flags --karmada-agent-image docker.io/karmada/karmada-agent:v1.12.0 --feature-gates=featuregateB=true will result in an error.