Docs: Feedback for Filtering Members with Attributes

Hi, I have some feedback about [this page](https://github.com/hazelcast/hz-docs/edit/main/docs/modules/maintain-cluster/pages/member-attributes.adoc)

The `HazelcastInstance` interface does not provide the `setAttribute(..)` method, so the code snippet is invalid:

```
HazelcastInstance member4 = Hazelcast.newHazelcastInstance();
// We can also set member attributes at runtime.
member4.setAttribute( "CPU_CORE_COUNT", "2" );
```

Are you sure it is still possible to do "or provide the member attributes at runtime via attribute setter methods on the Member interface."?

Open docs/modules/maintain-cluster/pages/member-attributes.adoc and review the Filtering Members with Attributes example. Check the HazelcastInstance and Member APIs to verify whether runtime attribute setters are available, then update the invalid snippet and the related runtime-attributes statement. Done means the example uses valid APIs and accurately describes supported behavior.

Written by the indexing model from the issue text.