sendBinlogDumpCommand: apply BinlogThroughGTID flag

[shlomi-noach]

Description

The current MySQL flavor implementation for ComBinlogDumpGTID does not populate the event flags, and sends just 0. When requesting a GTID position, the flags must include BinlogThroughGTID. This is then reflected when parsing the event:

vitess/go/mysql/binlog_dump.go

Lines 78 to 89 in 10ff5e3

	if flags2&BinlogThroughGTID != 0 {
	dataSize, pos, ok := readUint32(data, pos)
	if !ok {
	return logFile, logPos, position, readPacketErr
	}
	if gtid := string(data[pos : pos+int(dataSize)]); gtid != "" {
	position, err = replication.DecodePosition(gtid)
	if err != nil {
	return logFile, logPos, position, err
	}
	}
	}

If we don't populate the flag, we don't parse the GTID value.

this PR adds the necessary flag.

Furthermore, in compliance with MySQL server, we now actually also ignore the flag when parsing a ComBinlogDumpGTID packet. The datasize value is enough to determine that there is a GTID payload.

Related Issue(s)

Fixes #17579

Checklist

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

Deployment Notes

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[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 12 lines in your changes missing coverage. Please review.

Project coverage is 67.70%. Comparing base (cd94eff) to head (bc6770b).
Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
go/mysql/binlog_dump.go	0.00%	10 Missing ⚠️
go/mysql/flavor_mysql.go	75.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #17580   +/-   ##
=======================================
  Coverage   67.69%   67.70%           
=======================================
  Files        1585     1585           
  Lines      254827   254904   +77     
=======================================
+ Hits       172509   172574   +65     
- Misses      82318    82330   +12     

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