Add some target fields and move some things around (#3879)

In preparation for putting proxy code in the api package this creates some necessary fields in the target output and it pre-moves credential parsing and proxy handshake code to their new places. This will make the diff for the actual proxy code move quite a bit smaller.

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

internal/api/genapi/input.go

@@ -878,6 +878,11 @@ var inputStructs = []*structInfo{
 		outFile:     "targets/session_authorization.gen.go",
 		subtypeName: "SessionAuthorization",
 	},
+	{
+		inProto:     &targets.SessionAuthorizationData{},
+		outFile:     "targets/session_authorization_data.gen.go",
+		subtypeName: "SessionAuthorizationData",
+	},
 	{
 		inProto:     &targets.WorkerInfo{},
 		outFile:     "targets/worker_info.gen.go",