[Modules] Microsoft.Synapse/workspaces - adding 'systemAssignedPrincipalId' as output

[krbar]

Description

This PR resolves #3004 and adds the PrincipalId of the system-assigned identity as a new output systemAssignedPrincipalId.

Pipeline references

Pipeline

Type of Change

• New feature (non-breaking change which adds functionality)

Checklist

• I'm sure there are no other open Pull Requests for the same update/change
• My corresponding pipelines / checks run clean and green without any errors or warnings
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (readme)
• I did format my code