IPv6/dual-stack integration tests

[alpeb]

This adds a new test TestDualStack to the deep suite that ensures requests to a dual stack service are always routed the the IPv6 endpoint.

It also amends other tests in the suite for them to work in IPv6-only clusters:

• skipports: replaced the booksapp with emojivoto, given the servers in the former don't bind to IPv6 addresses
• endpoints: amended the regexes to include IPv6 addresses
• localhost: bumped nginx for it to bind to the IPv6 loopback as well

Note the TestDualStack test is disabled by default because Github runners don't support IPv6. To run it locally, first deploy a dual-stack cluster via:

kind create cluster --config test/integration/deep/kind-dualstack.yml

(for testing IPv6-only clusters, use the kind-ipv6.yml config)

Then load the images and trigger the test with:

bin/tests --name deep-dual-stack --skip-cluster-create $PWD/target/cli/linux-amd64/linkerd