Pod Security Standards: Usage of SHOULD and MUST

The web page https://kubernetes.io/docs/concepts/security/pod-security-standards/
should follow RFC 2119 in the use of SHOULD and MUST.

There are some occasions where the word "should is used but it's wrong:

In the section "Restricted":

> The following listed controls _should_ be enforced/disallowed:

In the table, entry "Privilege Escalation (v1.8+)":

> Privilege escalation (such as via set-user-ID or set-group-ID file mode) _should_ not be allowed.

The spec value lists no allowed values.

In both cases, it should be "MUST", not "should".

I recommend reviewing the use of should in the entire page, I only looked at the "restricted" section.

Start with the Pod Security Standards page at https://kubernetes.io/docs/concepts/security/pod-security-standards/ and review its use of “should” against RFC 2119. Correct the two identified statements in the Restricted section and inspect the rest of the page for similar SHOULD/MUST wording; done means the page uses the terms consistently with the specification.

Written by the indexing model from the issue text.