Update version to 8.3.0

Diff

• https://gitlab.com/gitlab-org/gitlab-qa/compare/v8.2.0...89d555821e4a35405336c59b9f5aec70302eac87

Release notes:

New scenarios and scenario updates

• UpdateFromPrevious scenario type for N - 1 vers... (!1015 - merged)
• Replace metrics OmnibusConfig with Scenario class (!1016 - merged)

Fixes

• Map Docker ports correctly in metrics.rb (!1017 - merged)

Other changes (CI, backstage)

• Remove unused env variables started with qa prefix (!1011 - merged)
• Add port mapping to gitlab docker instance (!1014 - merged)

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.