[Feature][scaleph-application-flink] support flink kubernetes operator ingress

[kalencaya]

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• I had searched in the feature and found no similar feature requirement.

Usage Scenario

now scaleph only support flink themself service expose and not support flink kubernetes operator ingress

Description

support flink kubernetes operator ingress

• update nginx-ingress-controller install docs
• add metallb install docs

Are you willing to submit a PR?

• Yes, I am willing to submit a PR!

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