Add initialize-with-vt-dba-tcp flag to enable TCP/IP connection access to the underlying MySQL instance

[yoheimuta]

Description

This PR adds initialize-with-vt-dba-tcp flag to vttestserver. If this flag is enabled, MySQL will be initialized with an additional user named vt_dba_tcp, who will have access via TCP/IP connection. The default value is false.

Related Issue(s)

Fixes #15267

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

[vitess-bot]

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[codecov]

Codecov Report

Attention: Patch coverage is 15.38462% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 65.42%. Comparing base (f82fb7c) to head (6f5e853).
Report is 36 commits behind head on main.

Files	Patch %	Lines
go/vt/vttest/toxiproxyctl.go	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15354      +/-   ##
==========================================
- Coverage   67.45%   65.42%   -2.03%     
==========================================
  Files        1560     1561       +1     
  Lines      193203   193605     +402     
==========================================
- Hits       130324   126670    -3654     
- Misses      62879    66935    +4056     

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[frouioui]

This looks good to me, thank you!

[GuptaManan100]

Rest LGTM