[Doc][Improve] Backlog increase during subscription replication

### 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?

When somebody uses [replicated subscriptions](https://pulsar.apache.org/docs/3.3.x/administration-geo/#replicated-subscriptions) sometimes can happen that there is a "ficticius" increase in backlog related to the [storing snapshots](https://github.com/apache/pulsar/wiki/PIP-33:-Replicated-subscriptions#storing-snapshots) overt the same topic if there are inactive subscriptions.

### What is your suggestion?

We need to add that information as a Note on that section.

### Any reference?

https://github.com/apache/pulsar/wiki/PIP-33:-Replicated-subscriptions#storing-snapshots

### Are you willing to submit a PR?

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

Start with the replicated subscriptions section in the Pulsar documentation and compare it with the linked PIP-33 “Storing snapshots” reference. Add a Note explaining the apparent backlog increase when inactive subscriptions are present; the work is done when that behavior is documented in the relevant section.

Written by the indexing model from the issue text.