VReplication: permission check logic on external tablets -- switch to a more practical solution

[rohit-nayak-ps]

Description

In #18348 we attempted to improve the logic for checking permissions on the source sidecar database. However there is one fundamental problem here that the vreplication users need permission on the mysql users table which can be a security red flag for certain users.

Another problem is that there are multiple ways of providing permissions including wild cards and role-based auth. Vitess users import from various different database versions as well, making it very hard to provide a single query to reliably test for permissions using, say just the information_schema tables.

This PR takes a different practical approach by attempting to test for permissions using dummy DMLs in a transaction to validate if permissions are present. This check is done on switching write traffic if reverse replication has been enabled.

We temporarily keep the old query around.

Related Issue(s)

#18349

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 or is not required

Deployment Notes

[vitess-bot]

Review Checklist

Hello reviewers! 👋 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]

Codecov Report

❌ Patch coverage is 0% with 72 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.47%. Comparing base (c024fff) to head (1a6be3f).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vttablet/tabletmanager/rpc_vreplication.go	0.00%	68 Missing ⚠️
go/vt/mysqlctl/fakemysqldaemon.go	0.00%	2 Missing ⚠️
go/vt/mysqlctl/mysqld.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18580      +/-   ##
==========================================
- Coverage   67.53%   67.47%   -0.06%     
==========================================
  Files        1613     1613              
  Lines      263780   263962     +182     
==========================================
- Hits       178144   178119      -25     
- Misses      85636    85843     +207     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[beingnoble03]

LGTM!

[mattlord]

LGTM! Just the one note about error handling and logging.

[shlomi-noach]

please merge main to resolve failing onlineddl_vrepl_suite checks.

[nickvanw]

LGTM with changes, thanks for adding tests!