[WIP] Drop support for (archived) Compose-on-Kubernetes

[thaJeztah]

carries #3139
closes#3139

closes#2967
(https://docker.atlassian.net/browse/IL-257 for internal tracker)

- What I did
Removed support for Kubernetes orchestrator, as required compose-on-kubernetes backend is archived

- How I did it
Code removal

- How to verify it
isn't this what CI is for ? :P

- Description for the changelog
Removed support for deprecated Compose-on-Kubernetes

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

Ok, at least some linting errors;

#17 66.46 cli/command/system/version.go:143:31: SA4017: HasKubernetes is a pure function but its return value is ignored (staticcheck)
#17 66.46 if orchestrator.HasKubernetes() {
#17 66.46 ^

And various (e2e) tests failing due to the kubernetes fields no longer being there;

=== FAIL: e2e/context TestContextImportTLS (0.05s)
context_test.go:62: assertion failed: --- expected
+++ actual
@@ -1,4 +1,4 @@
-NAME DESCRIPTION DOCKER ENDPOINT KUBERNETES ENDPOINT ORCHESTRATOR
-default * Current DOCKER_HOST based configuration unix:///var/run/docker.sock swarm
-test unix:///var/run/docker.sock https://kubernetes.docker.internal:6443 (default) swarm
+NAME DESCRIPTION DOCKER ENDPOINT ORCHESTRATOR
+default * Current DOCKER_HOST based configuration unix:///var/run/docker.sock swarm
+test unix:///var/run/docker.sock swarm
You can run 'go test . -test.update-golden' to automatically update testdata/context-ls-tls.golden to the new expected value.'

[thaJeztah]

Some failures remaining (and probably docs and completion scripts to be updated as well), but getting closer

--- FAIL: TestCreateInvalids (0.00s)
--- FAIL: TestCreateInvalids/orchestrator-all-no-endpoint (0.00s)
create_test.go:120: assertion failed: expected an error, got nil
--- FAIL: TestExportImportWithFile (0.00s)
export-import_test.go:23: assertion failed: error is not nil: context "test" does not exist
--- FAIL: TestExportImportPipe (0.00s)
export-import_test.go:49: assertion failed: error is not nil: context "test" does not exist
FAIL

[thaJeztah]

need to squash the commits, as the first commit doesn't build (removes github.com/docker/cli/cli/context/kubernetes, but it's still used in some places in that commit)

[thaJeztah]

Did a rebase;
These still fail, so need fixing;

 === FAIL: cli/command/context TestCreateInvalids/orchestrator-all-no-endpoint (0.00s)
create_test.go:120: assertion failed: expected an error, got nil
--- FAIL: TestCreateInvalids/orchestrator-all-no-endpoint (0.00s)
=== FAIL: cli/command/context TestCreateInvalids (0.00s)
=== FAIL: cli/command/context TestExportImportWithFile (0.00s)
export-import_test.go:23: assertion failed: error is not nil: context "test" does not exist
=== FAIL: cli/command/context TestExportImportPipe (0.00s)
export-import_test.go:49: assertion failed: error is not nil: context "test" does not exist