GithubPipeline: Allow customizing identity resource group and naming

[gambtho]

Description

When configuring a GitHub Actions pipeline for an AKS project, the managed identity is currently created in the cluster's resource group with a name derived from the Kubernetes namespace. This is inflexible for users who want to organize identity resources separately or who have naming conventions tied to project names.

Desired Behavior

• Allow users to customize the resource group where the managed identity is created, defaulting to rg-<projectName>
• Derive the identity name from the project name instead of the namespace (id-<projectName>-github)
• Show the full repo name (owner/repo) in the repo selector for clarity
• Ensure the identity resource group exists (create it if needed) before creating the managed identity
• Allow editing the identity resource group when retrying after an error

Acceptance Criteria

• Identity resource group field is editable in the Workload Identity setup step
• Default resource group is rg-<projectName>
• Identity name follows id-<projectName>-github pattern
• Resource group is created automatically if it doesn't exist
• Existing resource groups are not modified (skip creation)
• Repo selector shows owner/repo format
• Identity resource group field is accessible on error for retry
• Tests cover new az-cli helpers, hook logic, and component behavior