Document bidderSettings.storageAllowed (#3540)
Document bidderSettings.storageAllowed (#3540)

* Document bidderSettings.storageAllowed

See PBJS issue: https://github.com/prebid/Prebid.js/issues/7280 (and PR: https://github.com/prebid/Prebid.js/pull/7992)

* Update `bidderSettings.storageAllowed` documentation to make it clear how it interacts with other storage management settings

* Update version for introduction of `bidderSettings.storageAllowed`
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