Rewrite the Knative code-gen to a Go-native tool

[cardil]

Expected Behavior

To fix knative/infra#134 we need to remove the shell wrapper, so the Knative projects could run the code-gen in go run ... native way.

Actual Behavior

Current code gen has a shell wrapper. Because of it Knative projects which use this code gen require the vendor directory.

[dprotaso]

Note for a bunch of the codegen we do - it could be generics now

[Priyansurout]

/assign

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[cardil]

/reopen
/remove-lifecycle stale
/triage accepted

[knative-prow]

@cardil: Reopened this issue.

In response to this:

/reopen
/remove-lifecycle stale
/triage accepted

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