feat: Add random row generator in data generator

[advancedxy]

Which issue does this PR close?

Closes #.

Rationale for this change

Follow up of #426, supports generating random rows for specified struct type.

What changes are included in this PR?

Add utility method: generateRows to generate random rows.

How are these changes tested?

N/A.

[advancedxy]

@andygrove would you mind to take a look at this?

[andygrove]

LGTM overall. I think this is a good addition. I left a couple of small style suggestions.

[advancedxy]

Thanks everyone for reviewing.