fix: allow hostname to use subdomain with single label/character

[nothinux]

Fixes #4793

Release Notes:

[zhaohuabing]

@nothinux Thanks for fixing this! Could you please add a test to test/cel-validation/backend_test.go?

[nothinux]

added

[nothinux]

@zhaohuabing the coverage test failed because only 4 items are allowed. can we double this limit?

gateway/api/v1alpha1/backend_types.go

Lines 119 to 121 in a383dd9

	// +kubebuilder:validation:MaxItems=4
	// +kubebuilder:validation:XValidation:rule="self.all(f, has(f.fqdn)) || !self.exists(f, has(f.fqdn))",message="fqdn addresses cannot be mixed with other address types"
	Endpoints []BackendEndpoint `json:"endpoints,omitempty"`

[zhaohuabing]

@zhaohuabing the coverage test failed because only 4 items are allowed. can we double this limit?

gateway/api/v1alpha1/backend_types.go

Lines 119 to 121 in a383dd9

	// +kubebuilder:validation:MaxItems=4
	// +kubebuilder:validation:XValidation:rule="self.all(f, has(f.fqdn)) || !self.exists(f, has(f.fqdn))",message="fqdn addresses cannot be mixed with other address types"
	Endpoints []BackendEndpoint `json:"endpoints,omitempty"`

I think it's fine to make it 8 cc @guydc

[arkodg]

@zhaohuabing the coverage test failed because only 4 items are allowed. can we double this limit?

gateway/api/v1alpha1/backend_types.go

Lines 119 to 121 in a383dd9

	// +kubebuilder:validation:MaxItems=4
	// +kubebuilder:validation:XValidation:rule="self.all(f, has(f.fqdn)) || !self.exists(f, has(f.fqdn))",message="fqdn addresses cannot be mixed with other address types"
	Endpoints []BackendEndpoint `json:"endpoints,omitempty"`

I think it's fine to make it 8 cc @guydc

64, so it account for cases where users are auto generating Backend resources to route to custom backends ? Can we do that in a separate PR @nothinux ?