Docs: sso.rst still uses removed `airflow webserver --reload` command from Airflow 2

[Dotify71]

Description

While reading through the FAB auth manager SSO documentation, I found that the Single Sign-On (SSO) Integration page still references the airflow webserver CLI command, which was removed in Airflow 3 and replaced by airflow api-server.

File: providers/fab/docs/auth-manager/sso.rst

Line 148–152 (Step 5 of Configuration Steps):

5. **Restart Airflow Webserver**

   .. code-block:: bash

      airflow webserver --reload

Why this is a problem

Airflow 3 replaced airflow webserver with airflow api-server. A user following this SSO setup guide on Airflow 3 will run airflow webserver --reload and get a command not found error at the final step, which is particularly frustrating after completing all the OAuth2 configuration steps above it.

Proposed fix

• Replace airflow webserver --reload with airflow api-server (Airflow 3 equivalent)
• Update the step title from "Restart Airflow Webserver" to something like "Restart Airflow API Server"

This is similar to the fix already applied in configuring-flask-app.rst (see PR #68162).

Notes

I found this while reviewing the FAB auth-manager docs for Airflow 3 consistency. Happy to submit a PR for this fix.