local backend: fix steps having logs form other steps (#5582)

## problem

if steps where started concurrent, the stdout pipeline reader war overwritten and you randomly got the wrong command stream 
from a step.

## change

where we have possible race conditions, we now use thread save types
e.g. store the command struct and the output reader in sync.Map

also a lot of tests where added

pipeline/backend/local/clone.go

@@ -100,11 +100,19 @@ func (e *local) execClone(ctx context.Context, step *types.Step, state *workflow
 	cmd.Env = env
 	cmd.Dir = state.workspaceDir
 
-	// Get output and redirect Stderr to Stdout
-	e.output, _ = cmd.StdoutPipe()
-	cmd.Stderr = cmd.Stdout
+	reader, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
 
-	state.stepCMDs[step.UUID] = cmd
+	// Save state
+	state.stepState.Store(step.UUID, &stepState{
+		cmd:    cmd,
+		output: reader,
+	})
+
+	// Get output and redirect Stderr to Stdout
+	cmd.Stderr = cmd.Stdout
 
 	return cmd.Start()
 }