Bump default enterprise gateway image

[pmalek]

It seems that we've neglected the DefaultEnterpriseImageTag leaving it at 2.7

kubernetes-testing-framework/pkg/clusters/addons/kong/addon.go

Lines 50 to 51 in 6cfb2cb

	// DefaultEnterpriseImageTag latest kong enterprise image tag
	DefaultEnterpriseImageTag = "2.7.0.0-alpine"

The outcome of this, given that we use defaults in KIC:

https://github.com/Kong/kubernetes-ingress-controller/blob/3ce7c14afd2099e991c4dcd3370f23ef8c742a5e/test/internal/helpers/ktf.go#L18-L30

is that we've been skipping tests in KIC that we didn't intend to skip: https://github.com/Kong/kubernetes-ingress-controller/actions/runs/4086412787/jobs/7045676471#step:7:15296

=== Skipped
=== SKIP: test/integration TestIngressRegexMatchPath (0.00s)
    ingress_regex_match_test.go:32: regex prefixes are only relevant for Kong 3.0+

=== SKIP: test/integration TestIngressRegexMatchHeader (0.00s)
    ingress_regex_match_test.go:186: regex prefixes are only relevant for Kong 3.0+

=== SKIP: test/integration TestIngressClassRegexToggle (1.00s)
    ingress_test.go:565: legacy regex detection is only relevant for Kong 3.0+

=== SKIP: test/integration TestIngressRegexPrefix (0.00s)
    ingress_test.go:698: regex prefixes are only relevant for Kong 3.0+

=== SKIP: test/integration TestIngressRecoverFromInvalidPath (0.00s)
    ingress_test.go:861: the case TestIngressRecoverFromInvalidPath should be run separately; please set TEST_RUN_INVALID_CONFIG_CASES to true to run this case

=== SKIP: test/integration TestPluginOrdering (1.00s)
    plugin_test.go:207: plugin ordering requires Kong Enterprise 3.0+