As discussed during the alpha review, the ReadOnly field is not really
needed because volume mounts can also be read-only. It's a historical
oddity that can be avoided for generic ephemeral volumes as part
of the promotion to beta.

This is the result of "make update" minus the testdata update which
will be committed separately.

This is the result of
   UPDATE_COMPATIBILITY_FIXTURE_DATA=true go test k8s.io/api
after removing the ReadOnly field from the API. The test data
for older releases must be updated because the current code
no longer supports that field.

The removal itself is okay because the struct was declared
as alpha.

Because EphemeralVolumeSource is embedded quite a lot, different types
are affected. Here is one example:

       --- FAIL: TestCompatibility/extensions.v1beta1.DaemonSet/v1.20.0 (0.04s)
            compatibility.go:476: json differs
            compatibility.go:477:   string{
                  	... // 12941 identical bytes
                  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x7d, //  |               }|
                  	0x0a, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x7d, //  |.              }|
                - 	0x2c, 0x0a, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, // -|,.              |
                - 	0x22, 0x72, 0x65, 0x61, 0x64, 0x4f, 0x6e, 0x6c, 0x79, 0x22, 0x3a, 0x20, 0x74, 0x72, 0x75, 0x65, // -|"readOnly": true|
                  	0x0a, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x7d, 0x0a, 0x20, //  |.            }. |
                  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x7d, 0x0a, 0x20, 0x20, 0x20, 0x20, 0x20, //  |         }.     |
                  	... // 31426 identical bytes
                  }

            compatibility.go:482: yaml differs
            compatibility.go:483:   string{
                  	... // 22893 identical bytes
                  	0x34, 0x22, 0x0a, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x65, 0x70, 0x68, 0x65, 0x6d, //  |4".        ephem|
                  	0x65, 0x72, 0x61, 0x6c, 0x3a, 0x0a, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, //  |eral:.          |
                - 	0x72, 0x65, 0x61, 0x64, 0x4f, 0x6e, 0x6c, 0x79, 0x3a, 0x20, 0x74, 0x72, 0x75, 0x65, 0x0a, 0x20, // -|readOnly: true. |
                - 	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,                                           // -|         |
                  	0x76, 0x6f, 0x6c, 0x75, 0x6d, 0x65, 0x43, 0x6c, 0x61, 0x69, 0x6d, 0x54, 0x65, 0x6d, 0x70, 0x6c, //  |volumeClaimTempl|
                  	0x61, 0x74, 0x65, 0x3a, 0x0a, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, //  |ate:.           |
                  	... // 5965 identical bytes
                  }

            compatibility.go:488: proto differs
            compatibility.go:490:   (
                  	"""
                  	... // 459 identical lines
                  	                }
                  	              }
                - 	              2: 1
                  	            }
                  	          }
                  	... // 1083 identical lines
                  	"""
                  )

            compatibility.go:506: wrote expected compatibility data... verify, commit, and rerun tests

This is the result of
  UPDATE_BOOTSTRAP_POLICY_FIXTURE_DATA=true go test k8s.io/kubernetes/plugin/pkg/auth/authorizer/rbac/bootstrappolicy

Apparently enabling the GenericEphemeralVolume feature by default
affect this test. The policy that it now tests against is indeed
the one needed for the controller.