Return sandbox name based on day of week

What does this MR do and why?

Describe in detail what your merge request does and why.

Changes the default value of sandbox_name from gitlab-qa-sandbox-group to gitlab-qa-sandbox-group-n where n depends on the day of the week as returned by Time.now.wday (Monday=> 1 to Sunday=>7)

Should be merged together with !88290 (merged)

Related to https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/1315

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