Add scoped Variables

### Use case

Use a temporary regexp extractor, and make sure the variable name does not accidentally collide with other variable.

Currently, JMeter supports only global variables, which is a bad coding practice overall. We should lean towards scoped variables.

### Possible solution

Implement `Local Variables` config element that would specify variable names that would become "local" to the controller.

For instance:

```
Transaction Controller
Local Variables(names = {test})
Http Sampler
Regex Extractor(variable = {test})
```

### Possible workarounds

_No response_

### JMeter Version

5.5

### Java Version

_No response_

### OS Version

_No response_