Allow security classification to be unknown

[ChristaBull]

Idea Park your idea's here, they may become features!

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User story

As a user I want to be able to enter a metadata record without knowing the security classification.

Describe the idea

Currently a user is required to provide a security classification, and if they select an option and save have no way to identify they don't actually know the security classification. An option should be available to identify the classification is unknown.

[NicoledeGreef]

this is resolved by actioning #437