`kn apply` ignores revision name

### Bug report

Revision name is discarded -- note the revision name in the output below:

```shell
$ kn service apply --filename service.yaml --revision-name="foo-iamrevision"
Creating service 'foo' in namespace 'default':
...
Service 'foo' created to latest revision 'foo-00001' is available at URL:
http://foo.default.cluster.auth.dev
```

### Expected behavior

Expected it to behave like create in this scenario (note the revision name).

```
kn service create --filename service.yaml --revision-name="foo-iamrevision"
Creating service 'foo' in namespace 'default':
...
Service 'foo' created to latest revision 'foo-iamrevision' is available at URL:
http://foo.default.cluster.auth.dev
```

### Steps to reproduce the problem

Pretty much the steps above.

### kn version

`go installed` from f128d045ba2139d1113b46427a09366e131c6b7c

```
Version:
Build Date:
Git Revision:
Supported APIs:
* Serving
- serving.knative.dev/v1 (knative-serving v0.19.0)
* Eventing
- sources.knative.dev/v1alpha2 (knative-eventing v0.19.0)
- eventing.knative.dev/v1beta1 (knative-eventing v0.19.0)
```

### Knative (serving/eventing) version

> 0.19.x