[improve][doc] clarify detailed behaviors for failover (non-partitioned topics)

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### What issue do you find in Pulsar docs?

https://pulsar.apache.org/docs/next/concepts-messaging/#failover--non-partitioned-topics
Currently, our docs lack detailed explanations of how a consumer is selected.

### What is your suggestion?

1. Add missing docs and demonstrate the process with examples.

For example, if consumer 1 hash = 55, consumer 2 hash = 65, and topic name hash = 60, then this topic will be assigned to (? which) consumer?

2. Create some illustrations to vividly show the process (e.g., hash ring)

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I've discussed this with @codelipenghui that engineers need to read the source code and then provide tech inputs.

### Any reference?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!