improve performance by concurrently setting labels, reviewers and assignees

[Shubh Bapna]

Currently we are setting labels, reviewers and assignees one by one. See: https://github.com/kiegroup/git-backporting/blob/main/src/service/git/github/github-client.ts#L69

However, we can take advantage of promises here and trigger all the API calls concurrently and await them together. We can use Promise.all or Promise.allSettled