Expose peer certificates in round tripper response

[snehachhabria]

What type of PR is this?
Add one of the following kinds:

/kind test
/area conformance

What this PR does / why we need it:
This PR exposes the peer certificates from the http response in round tripper.

Which issue(s) this PR fixes:
Fixes ##3020

Does this PR introduce a user-facing change?:

NONE

[sunjayBhatia]

looks sufficient to capture the certs a backend may be presenting, i'm curious how this will be used in practice since there aren't any tests making assertions on this? I might be missing some context that needs to be added to the original issue, but if a backend is presenting an unexpected cert for example, we would likely get a TLS connection error and would never get to this captured response

[snehachhabria]

looks sufficient to capture the certs a backend may be presenting, i'm curious how this will be used in practice since there aren't any tests making assertions on this? I might be missing some context that needs to be added to the original issue, but if a backend is presenting an unexpected cert for example, we would likely get a TLS connection error and would never get to this captured response

currently there are no tests in the conformance that are asserting on this, exposing this will allow the extension of tests to make these assertions as well. That's right if an unexpected cert is provided there will be a TLS connection error and there is no need to validate the cert in that scenario but for success scenarios additional validation will help assert the cert details.

This was discussed in the meeting on Monday, I've added more context to the issue. Hope all this helps

[snehachhabria]

@sunjayBhatia if this PR looks good can it be merged ?

[robscott]

Thanks @snehachhabria, I think this is likely going to be helpful as we build out more Backend mTLS capabilities in the API. In the meantime, I think it's reasonable to let this in for anyone using this framework for broader test cases. Will defer to someone else for LGTM though.

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: robscott, snehachhabria

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[mlavacca]

Thanks, @snehachhabria!

/lgtm