Add workflow_run trigger to GitHubActionsAttribute

[ChrisonSimtian]

Adds a workflow_run trigger so a generated workflow can start after another workflow finishes (for example, test a deployed environment after the deploy workflow completes).

New GitHubActionsAttribute properties:

• OnWorkflowRunWorkflows (string[]): upstream workflow names. Setting it enables the trigger.
• OnWorkflowRunTypes (string[], default completed)
• OnWorkflowRunBranches (string[])
• OnWorkflowRunRequireSuccess (bool, opt-in): adds a job-level if: github.event_name != 'workflow_run' || github.event.workflow_run.conclusion == 'success' (so cron or dispatch runs of the same workflow are not skipped), since workflow_run also fires for failed or cancelled upstream runs. This needed a new Condition property on GitHubActionsJob, written as if: only when set.

Behaviour:

• New GitHubActionsWorkflowRunTrigger is a detailed trigger, so it combines with the other On* triggers and conflicts with shorthand On, via the existing assertion in GetConfiguration.
• OnWorkflowRunBranches or OnWorkflowRunRequireSuccess without OnWorkflowRunWorkflows throws, as do blank workflow names.
• Null OnWorkflowRunTypes or OnWorkflowRunBranches throws a clear error.
• With nothing set, output is unchanged (existing snapshots untouched).

Specs: a workflow-run snapshot in ConfigurationGenerationSpecs plus GitHubActionsWorkflowRunSpecs.

Base: develop, the default PR target. The change is non-breaking and the branch is a plain two-commit addition, so it can be cherry-picked onto the 10.4.x line for a patch release.