build: move e2e dependencies into e2e/go.mod

Several packages are only used while running the e2e suite. These
packages are less important to update, as the they can not influence the
final executable that is part of the Ceph-CSI container-image.

By moving these dependencies out of the main Ceph-CSI go.mod, it is
easier to identify if a reported CVE affects Ceph-CSI, or only the
testing (like most of the Kubernetes CVEs).

Signed-off-by: Niels de Vos <ndevos@ibm.com>

e2e/vendor/github.com/modern-go/concurrent/executor.go

@@ -0,0 +1,14 @@
+package concurrent
+
+import "context"
+
+// Executor replace go keyword to start a new goroutine
+// the goroutine should cancel itself if the context passed in has been cancelled
+// the goroutine started by the executor, is owned by the executor
+// we can cancel all executors owned by the executor just by stop the executor itself
+// however Executor interface does not Stop method, the one starting and owning executor
+// should use the concrete type of executor, instead of this interface.
+type Executor interface {
+	// Go starts a new goroutine controlled by the context
+	Go(handler func(ctx context.Context))
+}