Fallback to ngx.var.scheme for redirectScheme with use-forward-headers when X-Forwarded-Proto is empty

[flphvlck]

What this PR does / why we need it:

Annotation nginx.ingress.kubernetes.io/from-to-www-redirect is broken from v1.1.2 with use-forwarded-headers: true, when X-Forwarded-Proto is empty (the response from the Nginx Ingress Controller is invalid: Location: nil://www.demo.domain.tld).

This PR uses original way as fallback (d v1.1.2), when X-Forwarded-Proto is empty.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation only

Which issue/s this PR fixes

fixes #8462

How Has This Been Tested?

Testing is described in #8462.

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added tests to cover my changes.
• All new and existing tests passed.

[k8s-ci-robot]

@phidlipus: This issue is currently awaiting triage.

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[k8s-ci-robot]

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[k8s-ci-robot]

Hi @phidlipus. Thanks for your PR.

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[longwuyuan]

/ok-to-test

[longwuyuan]

/lgtm

[longwuyuan]

/assign @rikatz

[longwuyuan]

The release carrying this fix will be a few weeks later @phidlipus

[rikatz]

/approve
Tks

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: longwuyuan, phidlipus, rikatz

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