Make Pinniped compatible with Kube clusters which have enabled PSAs

Where possible, use securityContext settings which will work with the
most restrictive Pod Security Admission policy level (as of Kube 1.25).
Where privileged containers are needed, use the namespace-level
annotation to allow them.

Also adjust some integration tests to make similar changes to allow the
integration tests to pass on test clusters which use restricted PSAs.

test/integration/concierge_impersonation_proxy_test.go

@@ -949,6 +949,8 @@ func TestImpersonationProxy(t *testing.T) { //nolint:gocyclo // yeah, it's compl
 							Image:           env.ShellContainerImage,
 							ImagePullPolicy: corev1.PullIfNotPresent,
 							Command:         []string{"sh", "-c", "sleep 3600"},
+							// Use a restrictive security context just in case the test cluster has PSAs enabled.
+							SecurityContext: testlib.RestrictiveSecurityContext(),
 						},
 					},
 					ServiceAccountName: saName,
@@ -1090,6 +1092,8 @@ func TestImpersonationProxy(t *testing.T) { //nolint:gocyclo // yeah, it's compl
 						corev1.ResourceCPU:    resource.MustParse("10m"),
 					},
 				},
+				// Use a restrictive security context just in case the test cluster has PSAs enabled.
+				SecurityContext: testlib.RestrictiveSecurityContext(),
 			}}})
 
 			// Try "kubectl exec" through the impersonation proxy.

test/integration/whoami_test.go

@@ -1,4 +1,4 @@
-// Copyright 2020-2021 the Pinniped contributors. All Rights Reserved.
+// Copyright 2020-2022 the Pinniped contributors. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 package integration
 
@@ -176,6 +176,8 @@ func TestWhoAmI_ServiceAccount_TokenRequest_Parallel(t *testing.T) {
 					Image:           env.ShellContainerImage,
 					ImagePullPolicy: corev1.PullIfNotPresent,
 					Command:         []string{"sh", "-c", "sleep 3600"},
+					// Use a restrictive security context just in case the test cluster has PSAs enabled.
+					SecurityContext: testlib.RestrictiveSecurityContext(),
 				},
 			},
 			ServiceAccountName: sa.Name,