vtorc: Switch to Vitess stats

[dbussink]

This moves the stats setup to the internal Vitess stats package instead of another external dependency.

With this change we can remove the external dependency.

Checklist

• [x] "Backport to:" labels have been added if this change should be back-ported to release branches
• [x] 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 or is not required

[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 33.33333% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 68.42%. Comparing base (9cfd040) to head (ab1f0eb). Report is 1 commits behind head on main.

Files	Patch %	Lines
go/vt/vtorc/logic/vtorc.go	0.00%	5 Missing :warning:
go/vt/vtorc/inst/instance_dao.go	50.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15948      +/-   ##
==========================================
- Coverage   68.44%   68.42%   -0.03%     
==========================================
  Files        1562     1562              
  Lines      197055   197040      -15     
==========================================
- Hits       134876   134818      -58     
- Misses      62179    62222      +43     

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