Fix adding flags to vtctlclient and vtctldclient

[GuptaManan100]

Description

It was noticed that the flag parsing in vtctlclient and vtctldclient does not go through servenv.ParseFlagsFor. So all the places where we use servenv.OnParseFor, for these binaries don't end up actually adding the flags for them. Instead we have to add them directly on their main.go files.

This PR fixes this issue and adds test for their flags.

Related Issue(s)

• [VEP-4, phase 3] Switch flag definitions to be on pflag instead of flag and add make them package private. #10697

Checklist

• "Backport me!" label has been added if this change should be backported
• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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