feat: autogen GH workflows and split build, test, and publish (#971)

Closes https://github.com/ooni/probe/issues/2337.

GHGEN/main.go

@@ -0,0 +1,12 @@
+// Command GHGEN regenerates selected GitHub actions.
+package main
+
+import (
+	_ "embed"
+)
+
+func main() {
+	for name, jobs := range Config {
+		generateWorkflowFile(name, jobs)
+	}
+}