Add some sort of extension point in `CBORParser` for pluggable custom-tag support

(note: inspired by https://github.com/FasterXML/jackson-core/issues/1428)

Since tag system in CBOR is extensible, users may well want to use custom tags.
Although there is a very bare-bones accessibility mechanism with `CBORParser`, basically 2 methods:

```
public int getCurrentTag() {
return _tagValues.getFirstTag();
}

public TagList getCurrentTags() {
return _tagValues;
}
```

it would be good to have some sort of mechanism (callback(s)?) to allow some automation of handling -- to give low-level access to `CBORParser` state upon encountering tags (either ones not supported by Jackson CBOR module, or maybe all).

I don't know exactly how that should look like so help would be appreciated.