Fix symbol publishing

[snnn]

Description:

This pull request refactors the symbol publishing workflow that uses the internal REST API. It addresses a breaking change introduced by the Az.Accounts module update (v5.0.1+) where Get-AzAccessToken now returns a SecureString. Additionally, it improves the structure and robustness of the custom symbol publishing steps.

Problem:

1. The pipeline recently stopped working due to an update in the Azure PowerShell Az.Accounts module. The Get-AzAccessToken cmdlet now returns a SecureString by default, which was incompatible with the previous script that expected a plain string token when setting a pipeline variable.
2. The previous implementation used two separate tasks: one AzurePowerShell@5 task to generate the token and set it as a pipeline variable, and a subsequent pwsh task to consume this variable and make REST API calls. This separation required converting the SecureString to plain text before setting the pipeline variable.

Solution:

To address these issues and improve the pipeline's design:

1. The "Generate an Azure Token" (AzurePowerShell@5) task and the "Publish Symbols using internal REST API" (pwsh) task have been combined into a single AzurePowerShell@5 task.
2. Within this unified task:
   • Get-AzAccessToken is called, and its SecureString output is stored in a local PowerShell variable.
   • The SecureString token is converted to plain text only within the scope of this script and immediately before it's used in the Authorization header for Invoke-RestMethod calls.
   • The token is no longer passed between tasks via a pipeline variable, enhancing security by limiting the scope of the plain text token.

Key Changes:

• Enhanced SecureString Management: The token remains a SecureString for most of its lifetime within the script, reducing exposure.
• Improved Error Handling: try-catch blocks have been added around the token retrieval and Invoke-RestMethod calls for better error reporting and pipeline stability.
• Robust Parameter Handling: Explicit conversion for boolean parameters (e.g., includePublicSymbolServer) to ensure correct PowerShell boolean types before JSON serialization.