{ContainerApp} Add secret set examples for special characters

[vibhuanand]

Related command
az containerapp secret set

Description
This PR improves the help/docs examples for az containerapp secret set by adding non-trivial examples that demonstrate how to pass secret values containing spaces and special characters (e.g., ;, :, ", ') safely.
The current examples are trivial and don’t show quoting/escaping patterns that users commonly need in CI pipelines and interactive shells. This adds clear Bash and PowerShell examples for single and multiple secrets.

Fixes #32658

Testing Guide

1. Verify help content renders and the module loads:

   • python3 -m py_compile src/azure-cli/azure/cli/command_modules/containerapp/_help.py

2. (Optional functional validation if you have an Azure subscription + Container App)

   • Create/update secrets using the patterns shown:
     • Bash:
       • az containerapp secret set -n <app> -g <rg> --secrets 'connString=Server=tcp:myserver;User Id=my user;Password=P@ss w0rd;'
       • az containerapp secret set -n <app> -g <rg> --secrets 'displayName="Test User 08" <testuser08@something.com>' 'apostrophe=Bob'\''s secret'
     • PowerShell:
       • az containerapp secret set -n <app> -g <rg> --secrets 'connString=Server=tcp:myserver;User Id=my user;Password=P@ss w0rd;' 'displayName="Test User 08" <testuser08@something.com>' 'apostrophe=Bob''s secret'
   • Confirm the secrets were stored:
     • az containerapp secret list -n <app> -g <rg>

History Notes
N/A (documentation/help examples only; no customer-facing behavior change beyond improved examples)

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