feat: Enable sync-labels workflow for all terraform-azurerm-avm- repositories

[segraef]

Synchronize GitHub Labels Across Repositories

Similiar to Azure/bicep-registry-modules#1285 this pull request introduces a new GitHub Actions workflow that synchronizes GitHub labels (https://azure.github.io/Azure-Verified-Modules/governance/avm-standard-github-labels.csv) across all repositories starting with terraform-azurerm-avm- in the Azure organization. The workflow uses the Set-AvmGitHubLabels.ps1 script from the Azure Verified Modules project to manage the labels.

The workflow is divided into two jobs:

1. getrepos: This job uses the GitHub GraphQL API to fetch the names of all repositories in the Azure organization. The names are stored in a JSON array, which is passed to the next job as an output.

2. sync-labels: This job runs the Set-AvmGitHubLabels.ps1 script for each repository. The script is run in a PowerShell Core (pwsh) shell. The repository name is passed to the script as an argument.

The workflow uses a matrix strategy to run the sync-labels job in parallel for each repository. The terraform-azurerm-avm-template repository is excluded from the matrix.