refactor!: replace authorizer.Allowed method with PermissionSet

[GeorgeMac]

This is a proposal to change the shape of the Authorizer interface.
Each of our authorizers use a slice of Permissions to evaluate whether a single supplied permission is allowed. This changes that contract to simply return the set of permissions and allow the consumer to validate them itself. The Allowed method still exists, though now it just exists on the new type PermissionSet which is the slice of Permissions.

One advantage of this will be the ability to derive from an authorizer which organizations the authorizer has access to read or write without going via a URM service.

• CHANGELOG.md updated with a link to the PR (not the Issue)
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• Tests pass
• http/swagger.yml updated (if modified Go structs or API)
• Documentation updated or issue created (provide link to issue/pr)
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