Add support for some form struct based agent addon

[saswatamcode]

I would like to propose an idea for something like BuildStructAgentAddon, that takes in some interface{} which implements a Manifests() method which has default values and values you can pass in.

Essentially a downstream operator could just maintain the objects they manage as k8s structs instead of helm or Go templates, so such a function, makes it much easier for those operators to create agent addons based on pre-existing code. Also, has added benefit that linting/updating manifests/managing versions in Go is much easier.

[qiujian16]

sorry for late reply, would you give some examples on this?

[saswatamcode]

@qiujian16 sorry for the confusing issue, this was written during a meeting. But essentially I was looking for a way to achieve this https://github.com/open-cluster-management-io/addon-framework/blob/main/examples/helloworld/helloworld.go example without embedding YAML files/helm charts, and instead passing k8s Go structs.

cc: @thibaultmg @JoaoBraveCoding as they have been working closely with this for a while.