Bump to version 8.1.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v8.0.0...039b34d0b8ee1e855a4e0f780b080858d3673be2

• Release notes:

### New scenarios and scenario updates

- https://gitlab.com/gitlab-org/gitlab-qa/-/merge_requests/928 Add OpenSearch version support to the nightly pipeline.

### Other changes (CI, backstage)

- https://gitlab.com/gitlab-org/gitlab-qa/-/merge_requests/1002 Introduce Env variable QA_DOCKER_ADD_HOSTS
- https://gitlab.com/gitlab-org/gitlab-qa/-/merge_requests/1000 Use EE_LICENSE var in cloud activation scenario

• Checklist before merging:

  • Diff link is up-to-date.
  • Based on the diff, lib/gitlab/qa/version.rb is updated, according to SemVer.
  • Release notes are accurate.

• Checklist after merging:

  • Update the release notes for the newly created tag.