feat(kuma-cp): deprecate standalone mode

[jakubdyszkiewicz]

Checklist prior to review

This PR is partial implementation of #8449
It does not take into account transition from Zone CP to federated Zone CP (nothing changes here).

The default KUMA_MODE is now zone. You can still run as standalone however, it's immediately switched as zone with a warning.

Nothing really changes from a user perspective aside of that if they explicitly use KUMA_MODE=standalone, they will need to change it in future releases.

Multizone fails because of #8498

• Link to relevant issue as well as docs and UI issues -- Fix ability to start a zone without KDS and have it work like standalone #8189 Rollout of deprecation of Standalone mode and Zone mode as default #8191
• 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) --

[lahabana]

Nice!

[slonka]

There are still references to "standalone" mode in the codebase. You can find them by running:

grep -rI standalone .
./app/kumactl/cmd/install/install_control_plane_test.go:                Entry("--kds-global-address is used with standalone", errTestCase{
./app/kumactl/cmd/install/install_control_plane_test.go:                        extraArgs: []string{"--kds-global-address", "192.168.0.1:1234", "--mode", "standalone"},
./app/kuma-dp/pkg/dataplane/envoy/remote_bootstrap.go:                  log.Info("could not fetch bootstrap configuration, make sure you are not trying to connect to global-cp. retrying (this could help only if you're connecting to zone-cp or standalone).", "backoff", c
fg.ControlPlane.Retry.Backoff, "err", err.Error())
...

A more general note: instead of renaming current "zone" to "federated zone" (and "standalone" to just "zone") wouldn't it be easier for everyone to digest if we just named "standalone" a "standalone zone"? Just asking, I'm not very firm on this.

[slonka]

LGTM, please remember about the docs issue / PR.