Enhanced output for vexplain keys

[systay]

Description

This PR enhances the output of vexplain keys to provide more detailed information about column usage in SQL queries, while maintaining backwards compatibility. The additional information will aid in more accurate index suggestions and query optimization.

Changes

• Added operator information to join and filter columns
• Included select columns in the output

New Output Format

For a query such as:

SELECT u.foo, ue.bar, count(*) 
from user u, user_extra ue 
where user.name = 'Tony' and u.id = ue.user_id
group by u.foo, ue.bar

The output will be:

{
	"statementType": "SELECT",
	"groupingColumns": [
		"user.foo",
		"user_extra.bar"
	],
	"joinColumns": [
		"user.id =",
		"user_extra.user_id ="
	],
	"filterColumns": [
		"user.name ="
	],
	"selectColumns": [
		"user.foo",
		"user_extra.bar"
	]
}

Motivation

The additional information provided by this enhancement will allow for more precise index suggestions and query optimization tools. By including operator information and select columns, users can make more informed decisions about index creation and query structure.

Related Issue(s)

#16830

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

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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 60 lines in your changes missing coverage. Please review.

Project coverage is 69.44%. Comparing base (eab262e) to head (5bccc70).
Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/sqlparser/ast_funcs.go	43.01%	53 Missing ⚠️
go/vt/vtgate/planbuilder/operators/keys.go	91.95%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16892      +/-   ##
==========================================
+ Coverage   69.42%   69.44%   +0.01%     
==========================================
  Files        1571     1570       -1     
  Lines      203276   203606     +330     
==========================================
+ Hits       141125   141393     +268     
- Misses      62151    62213      +62     

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