You could write a deployment plugin that generated the manifests and committed them to git, and then a release plugin that uses the git ops tool. There isn’t anything in waypoint to address this workflow today otherwise.
In addition to writing your own plugin, there are a few ways to use some escape hatches already built-in to waypoint using some combination of the exec plugin (see example) and hooks.
Both of these approaches let you drop into you plugging into shell scripts that can do the steps you describe. Presumably you don’t need Waypoint to do the gitops step, but rather just get the files to git.