Add a build tag for the e2e test only

This was initially part of #4565 which was closed in favour of moving
integration tests, but the consensus was that the e2e test is a special
case.

The e2e test requires so much more ahead-of-time setup that our bazel
build flow special cases it by marking it manual. This is a `go test`
equivalent to that, which enables the e2e test to remain under the test/
directory while still allowing `go test ./test/...` to work generally
for all other tests.

We'll add make targets for the e2e tests down the road. For now, we add
the build tag and define it in bazel so this commit should be a no-op
in effect.

Signed-off-by: Ashley Davis <ashley.davis@jetstack.io>

test/e2e/BUILD.bazel

@@ -29,6 +29,9 @@ go_test(
     name = "go_default_test",
     srcs = ["e2e_test.go"],
     embed = [":go_default_library"],
+    gotags = [
+        "e2e_test",
+    ],
     tags = ["manual"],  # 'bazel test //...' should not run e2e tests
     deps = [
         "//pkg/logs:go_default_library",

test/e2e/e2e_test.go

@@ -1,3 +1,5 @@
+//go:build e2e_test
+
 /*
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