Use FQDN in the host field of Istio resources

[ysk24ok]

What this PR does / why we need it:

This PR enables the Istio VirtualService and DestinationRule to use FQDN in the host field, as Istio recommends doing so.

To avoid potential misconfiguration, it is recommended to always use fully qualified domain names over short names

Which issue(s) this PR fixes:

Fixes #4387

Special notes for your reviewer:

[seldondev]

Hi @ysk24ok. Thanks for your PR.

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[seldondev]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ukclivecox]

/test integration

[ukclivecox]

/test notebooks

[adriangonz]

Hey @ysk24ok ,

Apologies for the long delay to review this one.

Just had a look and changes look good! Integration tests seem to pass, so this should be ready to go.

Thanks a lot for your contribution! 🚀