Epic: Golang SDK for building functions

[mengqiy]

Forking from GoogleContainerTools/kpt-functions-catalog#196 (comment)

We currently have a SDK for TS. We should have a similar SDK in golang.
IMO it may look like kubebuilder. It should provide

• [WIP] Standard Go pkg for KRM function Design golang library for authoring KRM fn #2568
• scaffolds source files (including tests). User only need to fill in the funcion logic.
• a Dockerfile
• a usage doc template
• scaffold a Makefile that manages the build lifecycle including build binary, run tests, build and push images and etc.
• utilities to convert the usage markdown file to code. We can either pre-generate before compiling or convert it at runtime.

[mikebz]

@mengqiy any guess as to the size of this effort?

[mengqiy]

This task needs to be designed first and then implemented. We may want to break this task to smaller ones and we can use this one as an umbrella issue.

[mengqiy]

In Q4, we are focusing on improving the library (kyaml).

[khrisrichardson]

IMO it may look like kubebuilder

@mengqiy FWIW, I love this idea so that the function code can be decorated to produce a CRD validation schema among other useful side-effects ala controller-tools