Deprecate NGINX controller image 1.3.1 support

Summary

We're upgrading the default NGINX controller image to 1.11.2. But this new version requires new RBAC rules and some users set nginx-ingress.rbac.create: false to manage their own RBAC rules.

This users will have to add the RBAC rules before they migrate to 1.11.2. So we added a fallback mechanism to only deploy 1.3.1 if this Helm value is set as above. We've also added nginx-ingress.controller.image.disableFallback which defaults to false, which users that manage their own RBAC can set to true to make their deployments also use 1.11.2, after they're sure the new RBAC rules are in place.

We want to deprecate the 1.3.1 image support as well as the fallback mechanism as part of 17.5, so that we can remove this support completely and only use 1.11.2 which has many security benefits.

Initially we're targeting removing the 1.3.1 fallback mechanism in 17.8 (chart 8.8), but we're discussing extending it to the next major (chart 9.0).

The 1.3.1 support removal is now officially targeted to 18.0, which will likely be chart 9.0.