fix(MeshGateway): ensure that duplicate listeners are not added when crossMesh is enabled on a listener and Routes specify hostnames

[ttreptow]

In the cross-mesh case, the SNI string will be a kuma SNI string for the gateway service (e.g. edge-gateway{mesh=default,port=tcp-8080}). Thus it is not possible to distinguish hosts at the listener level and no filter chain sni matchers are added. This can lead to a duplicate listener filter chain being added if there are multiple hostnames to route.

Thus we truncate the gatewayHosts array to size 1 before creating the listener blocks.

Fixes #8076

Supersedes #8105

• The approach in my PR solves the problem in a way that leaves the door open for host-based cross-mesh routing (i.e. specifying mesh hostnames in MeshGatewayRoute). I have that working and will submit a follow on PR for it
• The tests in this PR are modified from the ones in fix(MeshGateway): ignore MeshGatewayRoute hostnames using cross mesh listeners #8105, the authorship of the original tests (@michaelbeaumont ) was lost in some git rebasing

Checklist prior to review

• Link to relevant issue as well as docs and UI issues --
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
  • Don't forget ci/ labels to run additional/fewer tests
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? (this GH action will add "backport" label based on these file globs, if you want to prevent it from adding the "backport" label use no-backport-autolabel label) -- I don't think this needs to be backported

[ttreptow]

I accidentally re-incorporated @michaelbeaumont 's changes while rebasing 🙈 . I'm going to push a fixed commit in a minute

[michaelbeaumont]

@ttreptow unfortunately you need to rebase and add the --signoff to satisfy the DCO

[michaelbeaumont]

Thanks @ttreptow !