Import labels from Jira project

Jira REST API has a dedicated endpoint to pull all the labels in a project https://developer.atlassian.com/cloud/jira/platform/rest/v2/#api-rest-api-2-label-get we can use that to import all labels in batches, cache them and link the issues to the specific label.

We have a dedicated stage for that as well Gitlab::JiraImport::ImportLabelsWorker app/workers/gitlab/jira_import/stage/import_labels_worker.rb