Use port 8080 for Katib UI

[vpavlin]

What this PR does / why we need it:

This PR changes the port used by katib-ui from 80 (needs root privileges) to 8080 so that we can run katib-ui on OpenShift with default security context.

As katib-ui already supports port configuration it is really just about changing manifests, but I have also changed the USER in Dockerfile as running as unprivileged user is generally considered a good practice in containers.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #966

Special notes for your reviewer:

1. Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

There is not a change of the image, but there is a change in the image, not sure if that fits under this note.

Release note:

NONE

---

This change is 

[k8s-ci-robot]

Hi @vpavlin. Thanks for your PR.

I'm waiting for a kubeflow member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[hougangliu]

/ok-to-test

[hougangliu]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hougangliu

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