Documentation on ingress.kubernetes.io/force-ssl-redirect is outdated

[jwnx]

What steps did you take and what happened:
Since #252, Contour leverages HttpsRedirect instead of RequireTls to enforce force-ssl-redirect. All documentation versions are affected.

What did you expect to happen:
The documentation would describe the correct behavior.

Anything else you would like to add:
The ingress.kubernetes.io/force-ssl-redirect annotation was introduced by #149 in Jan, 2018. Its documentation was first written in 9e166f3 on Fev 6th, 2018 and the #252 fix was merged on Feb 26th, 2018, but the documentation wasn't updated since then.

Environment:
N/A

[github-actions]

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[github-actions]

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