Create arrow timezone interface and wrapper

## Feature Request

It would be useful for users to directly import an arrow timezone object and create Arrow timezones rather than having to use `datetime.timezone`, `ZoneInfo`, or `dateutil.tz.gettz`. This will allow for full feature encapsulation within Arrow, so users can create timezones like this:

```python
import arrow
arrow.now(tz=arrow.timezone("US/Pacific"))
```

This `arrow.timezone` wrapper can simply wrap the `TzinfoParser` and `dateutil.tz.gettz` logic and expose an easy-to-use interface for users.