Add @mattlord as CODEOWNER for vtctld[client] related things

[mattlord]

Description

See title. 🙂 I've been doing more and more vtctldclient related work over recent months so I think it makes sense to add me as a CODEOWNER for related things.

Related Issue(s)

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

[vitess-bot]

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[frouioui]

Small error in the file (unrelated to your change)

Unknown owner on line 10: make sure @dkhenry exists and has write access to the repository

[mattlord]

Small error in the file (unrelated to your change)

Unknown owner on line 10: make sure @dkhenry exists and has write access to the repository

Good catch! He's no longer an active maintainer so I'll remove him from any lines in the file here.