quickstart cleanup

[nirrozenbaum]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
This PR does some cleanup to the quickstart guide.
two main changes:

• Helm is mentioned as a pre-requisite at the beginning of the guide. therefore, the helm requirement was removed from KGateway section.
• Istio DestinationRule is integrated into the helm chart (only when istio is selected as provider). therefore, it's no longer required to install it as part of the guide steps (or delete it). also, since DestinationRule is not used as a yaml anymore but part of the helm templates, the yaml file was deleted.
  Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

None

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nirrozenbaum

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• OWNERS [nirrozenbaum]

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[kfswain]

OOC: Does netlify not allow us to always use 1 on Ordered Lists, standard markdown does?

[nirrozenbaum]

I think I tried it once and it didn’t render as expected. I can try

[elevran]

IIRC, we used automumbering with netlify in a previous project and it worked

[kfswain]

/lgtm