Update event info to note that the workflow was triggered manually if the repo/title was not provided. Update description of workflow_dispatch argument to describe what it can be used for when triggering manually. Only run step to build URL to commit that triggered workflow if it was triggered from an external repo

Update event info to note that the workflow was triggered manually if the repo/title was not provided. Update description of workflow_dispatch argument to describe what it can be used for when triggering manually. Only run step to build URL to commit that triggered workflow if it was triggered from an external repo #4994