Run `hook` as a GitHub action

[BobyMCbobs]

What would you like to be added:
support for Hook to be run as a GitHub action

Why is this needed:
CNCF projects need Prow features without the complexity of Prow

ii is doing some POC'ing over here

• https://github.com/cncf-infra/prow-github-action
• https://github.com/cncf-infra/mock-project-repo

/cc @hh @Riaankl @RobertKielty
/assign @BobyMCbobs @hh @Riaankl @RobertKielty

[BobyMCbobs]

/sig k8s-infra

Update: this is wrong! Where does it belong? @hh

[BobyMCbobs]

/unsig k8s-infra

[BobyMCbobs]

/sig nil

[k8s-ci-robot]

@BobyMCbobs: The label(s) sig/nil cannot be applied, because the repository doesn't have them.

Details

In response to this:

/sig nil

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[BobyMCbobs]

Plan of action:

• build out a implementation of hook/server.go
• given /github/workflow/event.json and sufficient auth, create a http server using httptest and call the endpoint

Thoughts @hh?

[hh]

I like this

[hh]

httptest would get the plumbing up the quickest I think.

Alternatively we could create prow/cmd/pga as a rewrite of demuxEvent() that reads the payload from GITHUB_EVENT_PATH and directly switches on GITUB_EVENT_NAME calling the appropriate handleFOOEvent()

From https://docs.github.com/en/github-ae@latest/actions/learn-github-actions/environment-variables#default-environment-variables :

GITHUB_EVENT_NAME The name of the event that triggered the workflow. For example, workflow_dispatch.
GITHUB_EVENT_PATH The path to the file on the runner that contains the full event webhook payload. For example, /github/workflow/event.json.

Lift the case statement from demuxEvent() as prow/cmd/pga as the action: https://github.com/kubernetes/test-infra/blob/master/prow/hook/server.go#L91-L176