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Use pointer for PSP allow escalation
Fixes#53437
The `AllowPrivilegeEscalation` field was added to PodSpec and PodSecurityPolicySpec in 1.8.0.
In order to remain compatible with pre-1.8.0 behavior, PodSecurityPolicy objects created against a previous release must not restrict this field, which means the field must default to true in PodSecurityPolicySpec. However, the field was added as a `bool`, not a `*bool`, which means that no defaulting is possible.
We have two options:
1. Require all pre-existing PodSecurityPolicy objects that intend to allow privileged permissions to update to set this new field to true
2. Change the field to a `*bool` and default it to true.
This PR does the latter. With this change, we have the following behavior:
A 1.8.1+ client/server now has three ways to serialize:
* `nil` values are dropped from serialization (because `omitempty`), which is interpreted correctly by other 1.8.1+ clients/servers, and is interpreted as false by 1.8.0
* `false` values are serialized and interpreted correctly by all clients/servers
* `true` values are serialized and interpreted correctly by all clients/servers
A 1.8.0 client/server has two ways to serialize:
* `false` values are dropped from serialization (because `omitempty`), which is interpreted as `false` by other 1.8.0 clients/servers, but as `nil` (and therefore defaulting to true) by 1.8.1+ clients/servers
* `true` values are serialized and interpreted correctly by all clients/servers
The primary concern is the 1.8.0 server dropping the `false` value from serialization, but I consider the compatibility break with pre-1.8 behavior to be more severe, especially if we can resolve the regression in an immediate point release.
```release-note
PodSecurityPolicy: Fixes a compatibility issue that caused policies that previously allowed privileged pods to start forbidding them, due to an incorrect default value for `allowPrivilegeEscalation`. PodSecurityPolicy objects defined using a 1.8.0 client or server that intended to set `allowPrivilegeEscalation` to `false` must be reapplied after upgrading to 1.8.1.
```
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