Bump version to 5.2.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v5.1.1...06a60b4197aa81f7263c090e4294c4a4e32c2f17

Release notes:

• Add QA_CAN_TEST_PRAEFECT to all Praefect related jobs in .gitlab-ci.yml
• Add pass-through for QA_CAN_TEST_PRAEFECT and QA_PRAEFECT_REPOSITORY_STORAGE
• Reorganize docs a bit to consolidate QA_CAN_TEST* features
• Pass-through QA_PRAEFECT_REPOSITORY_STORAGE to specs defaulting to 'default'

New scenarios and scenario updates

• !413 (merged) Add support for additional praefect tests.

Doc changes

• !413 (merged) Add support for additional praefect tests.

• 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:

  • Create a tag for the new release version.