Replace Go model generation for open-cluster-management

[manusa]

Description

Part of #6130

Replace model generation for open-cluster-management module with new OpenAPI approach.

Note

For extension models there are going to be multiple conflicts with the previously generated code.

Tasks

• Remove build-helper-maven-plugin
• Remove maven-antrun-plugin from the generate profile
• Remove jsonschema2pojo-maven-plugin from the generate profile
• Consolidate all extension models to the same module (certmanager, tekton, and so on all have multiple model generator modules)
• Configure the openapi-model-generator-maven-plugin plugin to generate the specific classes.
• Remove the go-related files and directories (Makefile, cmd)
• Remove invocation from the generateModel.sh script