CLI: add support for experimental new filters API in trigger

### Feature request
As part of preparing the experimental new filters API to Beta (tracked here: https://github.com/knative/eventing/issues/5204), we should add support to `kn` to create these filters when creating a trigger.

### Use case

With the new filters API entering Beta, more users will want to try it out. It would be convenient for them if they can use `kn` to create them, instead of being required to use yaml files to try out the new filters.

### UI Example

```
kn trigger create mytrigger --new-filter filtertype=filtervalue
```

Start at the `kn trigger create` entry point and trace how trigger filters are parsed and sent to the API. Compare the experimental filters API in issue 5204 with existing trigger creation behavior. Done means users can create the new filters through the proposed CLI option, with the resulting trigger accepted by the API.

Written by the indexing model from the issue text.