Remove FederatedIngress feature

[hectorj2f]

What this PR does / why we need it:

This PR removes one of the alpha features FederatedIngress. This feature should not be part of kubefed core as mentioned in #1284. The main intention is to remove from kubefed those features that are not part of its core functionalities, and consequently mark kubefed as beta.

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 #

#1284
Special notes for your reviewer:

[irfanurrehman]

Thanks @hectorj2f.
The TOC in userguide still has reference to ingress dns. You might need to update the TOC.
Rest LGTM.

[hectorj2f]

@irfanurrehman Thanks for the review 😍 . I'll address that reference and move forward with the rest of pending tasks.

[irfanurrehman]

LGTM for me. Leaving it for another set of eyes to have a check.
@makkes @jimmidyson

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hectorj2f, makkes

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[makkes]

lgtm but my experience with this feature is limited so I'll leave the last call to @jimmidyson.

[jimmidyson]

/lgtm

Thanks @hectorj2f for this and for the reviews @irfanurrehman and @makkes!