add support for vtgate traffic mirroring (queryserving)

[maxenglander]

Description

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

Related Issue(s)

https://github.com/vitessio/vitess/issues/13772 https://github.com/vitessio/vitess/pull/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
• [x] Tests were added or are not required
• [x] Did the new or modified tests pass consistently locally and on CI?
• [x] Documentation was added: https://github.com/vitessio/website/pull/1744

Deployment Notes

[vitess-bot[bot]]

Review Checklist

Hello reviewers! :wave: Please follow this checklist when reviewing this Pull Request.

General

• [ ] Ensure that the Pull Request has a descriptive title.
• [ ] Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• [ ] Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• [ ] Apply the release notes (needs details) label if users need to know about this change.
• [ ] New features should be documented.
• [ ] There should be some code comments as to why things are implemented the way they are.
• [ ] There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• [ ] Is this flag really necessary?
• [ ] Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• [ ] Each item in Jobs should be named in order to mark it as required.
• [ ] If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• [ ] Protobuf changes should be wire-compatible.
• [ ] Changes to _vt tables and RPCs need to be backward compatible.
• [ ] RPC changes should be compatible with vitess-operator
• [ ] If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• [ ] vtctl command output order should be stable and awk-able.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 75.06361% with 98 lines in your changes missing coverage. Please review.

Project coverage is 68.88%. Comparing base (fae7540) to head (43b8c1a). Report is 35 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtgate/vindexes/vschema.go	79.08%	32 Missing :warning:
go/vt/vtgate/vcursor_impl.go	23.52%	26 Missing :warning:
go/vt/vtgate/planbuilder/operators/mirror.go	50.00%	17 Missing :warning:
go/vt/vtgate/engine/mirror.go	79.31%	12 Missing :warning:
go/vt/vtgate/planbuilder/operator_transformers.go	80.00%	2 Missing :warning:
go/vt/vtgate/planbuilder/operators/ast_to_op.go	88.88%	2 Missing :warning:
go/vt/vtgate/semantics/semantic_table.go	90.00%	2 Missing :warning:
go/vt/vtgate/semantics/vtable.go	0.00%	2 Missing :warning:
go/test/vschemawrapper/vschema_wrapper.go	87.50%	1 Missing :warning:
go/vt/vtgate/planbuilder/operators/horizon.go	0.00%	1 Missing :warning:
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15992      +/-   ##
==========================================
+ Coverage   68.87%   68.88%   +0.01%     
==========================================
  Files        1562     1564       +2     
  Lines      200624   201012     +388     
==========================================
+ Hits       138179   138470     +291     
- Misses      62445    62542      +97     

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[maxenglander]

@systay thanks for the review! resolved all your comments except one, where i think i need a bit more guidance.

[deepthi]

Not sure why DCO check is still pending. I assume all the commits are correctly signed off. @maxenglander if you can confirm that, we can bypass and merge instead of a force-push -> Run CI all over again -> merge.

[maxenglander]

Hey @deepthi all the commits have the "Verified" sign on GH, and each commit individually has the Signed-off-by trailer from either [email protected] or (for ones I merged from GH) [email protected], both of which are attached to my GH account. Not sure if there's something else I need to do to verify.