add support for mirror routingrules (queryserving)

[maxenglander]

Description

Query-serving component for vitessio#15945. Do not merge before vitessio#15945. After vitessio#15945 is merged, rebase this PR on main.

Related Issue(s)

vitessio#13772
vitessio#15945

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added: document mirror rules vitessio/website#1744

Deployment Notes