Actors example implements non-existent code

**Describe the bug**

In the documentation found [here](https://docs.dapr.io/developing-applications/sdks/go/go-client/#actors) the documentation lists a struct wrapping the class `actors.Actor` which is not implemented in the go-sdk. The go-sdk implements client and server, but no class `actors.Actor`

**To Reproduce**

Go to the page, read the page, attempt to follow the example creating code like:

```
type ExampleActor struct {
actors.Actor
}
```

Observe the error: `undefined: actors`

**Expected behavior**

The documentation matches the implemented code, and does not implement go classes that cannot be inherited.

The go-sdk implements `actor` not `actors` and has no exported member `Actor` that can be inherited by a struct.


Open the Actors section at the linked Dapr Go SDK documentation page and compare its example with the implemented Go SDK actor client and server APIs. Update the example so it uses only exported, implemented Go SDK members, then verify that the displayed code no longer refers to `actors.Actor` or the undefined `actors` package.

Written by the indexing model from the issue text.