docs(MADR): reachable/autoreachable services with Mesh*Service

[lukidzi]

Checklist prior to review

We aim to provide feature parity for MeshService and MeshExternalService. One of the missing features is reachable services, and the goal is to provide some ideas and determine the best way to achieve that.

xrel: #10602

• 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) --

[lukidzi]

I am not yet fully certain if this is necessary, as the name might already include this functionality. The name is a bit tricky because, once it's synced, it has a hash and namespace appended, which can cause a lot of confusion.

[michaelbeaumont]

I think this should align with the backendRef of routes ultimately, right?

[lukidzi]

It should, but I feel it might not. Currently, backendRef in a dataplane's outbound has a name in the format name-hash.namespace (hash when synced), while backendRef in a route has name-hash with the namespace in a separate field. That's why I am considering doing the same for outbounds.