implement testEnv for e2e tests

.github/workflows/e2e.yaml

Makefile

cmd/flux/install_test.go

cmd/flux/main_test.go

cmd/flux/testdata/install/install_extra_components.golden

cmd/flux/testdata/install/install_no_args.golden

cmd/flux/testdata/uninstall/uninstall.golden

...flux/testdata/uninstall/uninstall_extra_components.golden

cmd/flux/trace_test.go

go.sum

internal/flags/crds_test.go

internal/flags/decryption_provider_test.go

internal/flags/ecdsa_curve_test.go

internal/flags/git_implementation_test.go

internal/flags/helm_chart_source_test.go

internal/flags/helm_release_values_test.go

internal/flags/kustomization_source_test.go

internal/flags/log_level_test.go

internal/flags/public_key_algorithm_test.go

internal/flags/rsa_key_bits_test.go