Fix vtbackup binary by adding the flags it needs that we missed before

[GuptaManan100]

Description

This PR adds the flags that vtbackup needs but we missed to add them during the flag work. These were found because of VTop failures while running the backup end to end tests.

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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[mattlord]

I would think vtbackup, vttablet, and maybe vtctld need backup flags. We can pare this down later.

[GuptaManan100]

Honestly, I have no idea. Maybe @deepthi or @rsajwani know 🤷‍♂️

[GuptaManan100]

I am going ahead and merging this PR, because I want the latest lite image to be built so that I can continue testing planetscale/vitess-operator#324. We can add these flags to vttablet and vtctld in a follow up PR if needed.

[deepthi]

We have to do the opposite, i.e, remove the other binaries: mysqlctl, vtexplain etc.
Not sure whether vtcombo and vttestserver are supposed to support backups.

[rsajwani]

vtbackup, vttablet, and m

Yes vttablet , vtctld will also need backup flags.

[rsajwani]

LGTM