Remove snippets created via Browser UI

What does this MR do and why?

Describe in detail what your merge request does and why.

Adds cleaning up of snippet artifacts in tests that create them via Browser UI. Adds an ability to retrieve snippet ids from UI after creation and then uses it to remove them via API after test execution. Also some general test refactoring to align with our best practices.

See last task of https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/763

MR acceptance checklist

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