Fix flag template when both visible and explicit flags are specified

[soltysh]

What type of PR is this?
/kind bug

What this PR does / why we need it:
Before the change the help might end up looking like this:

Options:
  -u, --username='': Username, will prompt if not providedn      --certificate-authority='': Path to a cert file for
the certificate authority

Notice no newline after --username flag description because trimRight is removing this. With this change we conditionally add new line after visibleFlags, which results in following output:

Options:
  -u, --username='': Username, will prompt if not provided
      --certificate-authority='': Path to a cert file for the certificate authority

Special notes for your reviewer:
/assign @juanvallejo

Does this PR introduce a user-facing change?:

Fix --help flag parsing 

[soltysh]

/sig cli
/priority important-longterm

[k8s-ci-robot]

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[juanvallejo]

/lgtm