Add SupportedFeature for port 8080 on Gateway

[xtineskim]

What type of PR is this? /kind test /area conformance

What this PR does / why we need it:
Conformance tests only use ports 80 and 443 in base manifests. This PR removed the Gateway w/ port 8080 in the base.yaml manifest, adds it to the tests yaml that was using it, and adds a SupportedFeature for port 8080

Which issue(s) this PR fixes:

Fixes ##2094

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Hi @xtineskim. Thanks for your PR.

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[xtineskim]

not 100% sure if it should be added to this section - open to suggestions

[robscott]

Makes sense to me, thanks!

[robscott]

Thanks @xtineskim!

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: robscott, xtineskim

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[mlavacca]

@robscott, is there any particular reason why this is not included in 0.8.0?
#2345 is also related to this.