[BUG] Description for TA-000026 misleading

### Describe the bug

Rule TA-000026's description is "Service Fabric clusters should **only** use Azure Active Directory for client authentication". However, the actual rule evaluation specifically just evaluates whether AAD client auth is enabled. It does not evaluate whether other types of client auth are disabled. Service Fabric clusters also have client certificate auth in addition to AAD client auth ([see docs](https://learn.microsoft.com/en-us/azure/templates/microsoft.servicefabric/clusters?pivots=deployment-language-arm-template#property-values-1)).

Is the original intent of the rule to just check whether AAD client auth is enabled or whether AAD client auth is the **only** client auth enabled?

### Expected behavior

Based off the current description, the rule should also validate that client certificate authentication is not enabled in addition to AAD client auth being enabled. Otherwise, the description should be updated to reflect the functionality of the rule's evaluation and simply state that the rule checks whether AAD client auth is enabled.

### Reproduction Steps

N/A

### Environment

N/A

Start by locating the TA-000026 rule definition and its evaluation logic, then compare the description with the current AAD client-authentication check. Resolve whether the rule should require AAD exclusively or only require it to be enabled, and update the rule or its description accordingly. Add or adjust coverage for the chosen behavior if the repository provides relevant tests.

Written by the indexing model from the issue text.