[Doc] admin api permissions does not include tenant administration

### 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?

[This](https://pulsar.apache.org/docs/next/admin-api-permissions/) piece of documentation does not include any reference to tenant administration (e.g. using the `pulsar-admin tenant update` command to update administrator roles). It seems like it should be included here.

### What is your suggestion?

It would be great to include references to the tenant administration directly in this documentation and to show examples of its usage.

### Any reference?

The tenants page has a reference to the update command which would be nice to include in this documentation as well. See [here](https://pulsar.apache.org/docs/3.0.x/admin-api-tenants/#update).

### Are you willing to submit a PR?

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

Start with the admin API permissions documentation linked in the issue, then compare it with the tenants page's update section. Add tenant administration references and usage examples for updating administrator roles with pulsar-admin tenant update. Done means the permissions documentation covers tenant administration and matches the existing tenants guidance.

Written by the indexing model from the issue text.