Adds support of named ports for kubectl port-forward

[m1kola]

What this PR does / why we need it:

Adds support of named ports for kubectl port-forward, so users will be able to run commands like this:

kubectl port-forward http-server http
kubectl port-forward http-server :http
kubectl port-forward http-server 8000:http

Same will work with services (including translation of the service's port into the pod's port).

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 kubernetes/kubectl#538

Special notes for your reviewer:

Please, note that this PR also includes #69403 which needs to be reviewed and merged first (it makes an util function to be exportable, so we can use it in the port-forward command).

Release note:

It is now possible to use named ports in the `kubectl port-forward` command

/sig cli
/kind feature

[juanvallejo]

nit: just return "" for the second value here

I see, missed the use-case for returning the same value here in the changes below

[m1kola]

Rebased

[krmayankk]

/ok-to-test

[m1kola]

/retest

[juanvallejo]

nit, just return nil, err here

[m1kola]

Thanks, updated.

[juanvallejo]

@m1kola thanks for the PR.
cc @soltysh for approval

/lgtm

[juanvallejo]

@m1kola please squash into single commit

[m1kola]

@juanvallejo please, re-approve. I rebased and squashed.

Sorry for this. I tried to split PR into multiple smaller PRs for easier review.

[juanvallejo]

/lgtm

[m1kola]

/retest

[soltysh]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: m1kola, soltysh

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