yimoucao

Fix #4287: add WorkloadGroup for istio v1alpha3 generator

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## Description Fix #4287 ## Type of change - [ ] Bug fix (non-breaking change which fixes an issue) - [x] Feature (non-breaking change which adds functionality) - [ ]...

istio Timestamp type should be mapped to String type in java

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### Describe the bug in istio generators, there's such code block that converts istio Timestamp to Long ```go manualTypeMap := map[reflect.Type]string{ reflect.TypeOf(types.BoolValue{}): "java.lang.Boolean", reflect.TypeOf(types.DoubleValue{}): "java.lang.Double", reflect.TypeOf(types.Duration{}): "java.lang.String", reflect.TypeOf(types.Timestamp{}): "java.lang.Long", reflect.TypeOf(types.Int32Value{}):...

istio WorkloadGroup is missed out

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### Is your enhancement related to a problem? Please describe no ### Describe the solution you'd like add it to istio's generators ### Describe alternatives you've considered _No response_ ###...