[BUG] Replace AnchorExtractor:toString with a identifier method

### Willingness to contribute

Yes. I can contribute a fix for this bug independently.

### Feathr version

All

### System information

- **OS Platform and Distribution (e.g., Linux Ubuntu 20.0)**:
- **Python version**:
- **Spark version, if reporting runtime issue**:

### Describe the problem

The toString method in AnchorExtractor and related classes is used as an identifier to group anchor features, which should be avoided. An identifier method should be created for this purpose.

### Tracking information

_No response_

### Code to reproduce bug

_No response_

### What component(s) does this bug affect?

- [ ] `Python Client`: This is the client users use to interact with most of our API. Mostly written in Python.
- [ ] `Computation Engine`: The computation engine that execute the actual feature join and generation work. Mostly in Scala and Spark.
- [ ] `Feature Registry API`: The frontend API layer supports SQL, Purview(Atlas) as storage. The API layer is in Python(FAST API)
- [ ] `Feature Registry Web UI`: The Web UI for feature registry. Written in React