[release-1.0] External controlplane e2e test

[istio-testing]

Manual cherrypick required.

#676 failed to apply on top of branch "release-1.0":

Applying: e2e multicluster test improve
Using index info to reconstruct a base tree...
M	docs/README.md
M	pkg/istioversion/version.go
M	tests/e2e/ambient/ambient_suite_test.go
M	tests/e2e/controlplane/control_plane_suite_test.go
M	tests/e2e/dualstack/dualstack_suite_test.go
M	tests/e2e/multicluster/multicluster_suite_test.go
M	tests/e2e/multicontrolplane/multi_control_plane_suite_test.go
M	tests/e2e/operator/operator_suite_test.go
M	tests/e2e/util/common/e2e_utils.go
A	tests/e2e/util/env/env.go
M	tests/e2e/util/istioctl/istioctl.go
Falling back to patching base and 3-way merge...
Auto-merging tests/e2e/util/istioctl/istioctl.go
Auto-merging tests/e2e/util/common/e2e_utils.go
Auto-merging tests/e2e/operator/operator_suite_test.go
Auto-merging tests/e2e/multicontrolplane/multi_control_plane_suite_test.go
Auto-merging tests/e2e/multicluster/multicluster_suite_test.go
CONFLICT (content): Merge conflict in tests/e2e/multicluster/multicluster_suite_test.go
Auto-merging tests/e2e/controlplane/control_plane_suite_test.go
CONFLICT (content): Merge conflict in tests/e2e/controlplane/control_plane_suite_test.go
Auto-merging pkg/env/env.go
Auto-merging docs/README.md
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 e2e multicluster test improve

[fjglira]

Not needed anymore