NGINX: add X-Original-Forwarded-Host header

[clementnuss]

adds the equivalent of the existing X-Original-Forwarded-For header but for the X-Forwarded-Host instead.
typically helps in the context of configuration snippet deprecation, as there is currently no safe way to add this header when it was already set upstream

What this PR does / why we need it:

with nginx controller version 1.12.0, configuration snippets are considered Critical per default and not allowed anymore. as a result, some users who relied on config snippets to set an X-Original-Forwarded-Host header are left without a solution.

this PR adds the X-Original-Forwarded-Host per default, akin to the existing X-Original-Forwarded-For header. Those headers are used to pass the original X-Forwarded-{For,Host} further to the upstream.

ℹ️ it would be nice to cherry-pick this commit back to release/v1.12 if it gets merged.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• CVE Report (Scanner found CVE and adding report)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation only

How Has This Been Tested?

I tested the implementation locally and added an e2e test to cover this new header.

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added unit and/or e2e tests to cover my changes.
• All new and existing tests passed.

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[k8s-ci-robot]

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[clementnuss]

I modified a series of test that were using assert.Contains(...,"host=myhost") and switched to using a regexp that checks whether we have a whitespace before host, as otherwise the new x-original-forwarded-host=myhost header will trigger the Contains expression.

the logic can be checked here: https://go.dev/play/p/cgkKxJZtCCp

in the current state I believe that the tests should pass, the one that failed looks like a false positive to me.

also sorry for abusing github action to run the tests, but locally on my arm64 mac it was complicated to run the e2e tests.

[clementnuss]

hi @Gacko

sorry for the ping, I would just need to know whether there's a chance this PR gets merged or not (even if it only lands in 1.13).

then based on your feedback, we will have to decide wether we keep allowing configuration snippet as fallback 😟 to generate this X-Original-Forwarded-Host header, or if we start building a custom nginx release until this PR gets merged 🤞🏼

also please let me know if it needs more tests or anything else.