Protect ExecuteFetchAsDBA against multi-statements, excluding a sequence of CREATE TABLE|VIEW.

[shlomi-noach]

Description

Addresses #14952 and to some extent #14949.

In this PR:

• ExecuteFetchAsDBA generally rejects any multi-statement SQL. For example, the following returns an error:

vtctldclient ExecuteFetchAsDBA zone1-0000000100 "select 1 from dual; select 2 from dual"

• We make an exception when all queries are of the form CREATE TABLE or CREATE VIEW. This is to accommodate the already existing use case of ApplySchema --batch-size.
• While at it, we also fix the allowZeroInDate parsing error as per Bug Report: ApplySchema --batch-size fails to apply zero-date and causes premature ReloadSchema #14952

Today, it is possible to send multiple queries in vtctldclient ExecuteFetchAsDBA. This potentially makes the connection pool dirty, as connections in the pool could have undrained result sets from previous calls.

Added tests.

This should be backported to:

• v18 to fix ApplySchema --batch-size, as well as to fix the dirty connection pool issue.
• v17 and v16 to fix the dirty connection pool issue.

Related Issue(s)

• Bug Report: ApplySchema --batch-size fails to apply zero-date and causes premature ReloadSchema #14952

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]

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[shlomi-noach]

This PR solves the issue for main, and for backports. Going forward, we will offer new RPC calls in v19, to completely replace the existing logic in v20.

[shlomi-noach]

There's a coupe of tests running ExecuteFetchAsDBA with sequences of commands such as STOP SLAVE; RESET SLAVE ALL; RESET MASTER etc. Fixing those.

[codecov]

Codecov Report

Attention: 24 lines in your changes are missing coverage. Please review.

Comparison is base (eddb39e) 47.29% compared to head (20658c8) 47.25%.
Report is 9 commits behind head on main.

Files	Patch %	Lines
go/vt/vttablet/tabletmanager/rpc_query.go	58.69%	14 Missing and 5 partials ⚠️
go/vt/sqlparser/utils.go	78.57%	2 Missing and 1 partial ⚠️
go/vt/schemadiff/schema.go	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14954      +/-   ##
==========================================
- Coverage   47.29%   47.25%   -0.05%     
==========================================
  Files        1137     1138       +1     
  Lines      238684   238898     +214     
==========================================
- Hits       112895   112883      -12     
- Misses     117168   117407     +239     
+ Partials     8621     8608      -13     

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[shlomi-noach]

Looking for a 2nd review 🙏

[shlomi-noach]

Backporting was expected to have merge conflicts. Will fix one by one.